I am not much of a music type so anything I know tends to come from the video world, fortunately remastering is part of that so I would like to think I can at least hang in such circles. I am not familiar in the slightest with the software you mention (to the point that I would not have been able to tell you what they do if someone had asked me) so I will avoid commenting there, if they are high end as you seem to imply then it should not be a problem (ironically it is the fancy GUI based stuff they bundle with machines sometimes that is the problem).
First thing: on any part of a machine you can spend absolutely silly money for what amounts to little or no gain. You will also be faced with a "for just €15 more" problem.
Audio: are you going for a nice creative thing with front audio ports:
http://uk.europe.creative.com/products/pro...559&listby= (not necessarily this model specifically but it is a nice illustration).
Or are you going to "suffer" a line in and a mic port (presumably with something fancy in the mixing deck side of things on the outside)?
I mention this for while there are nice the cost means I will have to switch up what I suggest doing. For all of the flame/holy wars I would argue that analogue to digital conversion (what your sound card is doing) has been more than most people are able to detect in just about everything as of about 5 years ago and you would sooner get a better capture from a better mic and/or room layout.
Frankly any modern piece of hardware should be able to hold it in half decent audio engineering circles especially if you only need to "record", if you need to record and filter at the same time then problems might arise.
Things to consider: audio, especially uncompressed which most self respecting audio engineers will use, will take up a considerable amount of space but more importantly do so at a rapid rate (you want a fast drive or maybe two*/a RAID if you are doing multiple instruments to different "tracks"). Conventional magnetic drives should be OK, 7200 RPM and no need to spring for SSD right now.
*one for the OS, one for the work, RAID stitches two or more drives together to make a virtual drive that is usually faster and assuming you are not using RAID0 with some error prevention.
I would sooner spend €15 or less and wire myself up a front panel or something like it from parts in an electronics shop: I assume you are still on the "phono" jacks, 3.5mm jacks and other TRS stuff which are all more or less the same thing:
http://pinouts.ru/Home/Tele35s_pinout.shtml . If your reply is something along the lines of "electronics is hard" I would politely tell you this is 3 wires per "component" and then suggest you never take yourself on the road either- you also get to be an insufferable bore when in bars in years to follow when you say things like "I built my own equipment back when".
"movie watching [and] general internet surfing/work" with the exception of H264 can be taken care of by just about anything made in the last 10 years if you know how to set it up so I will not linger on it. H264 should not be a problem on anything I lay out either.
Games if you will excuse the unintentional pun are a game changer although I will say things have evened out immensely in the last few years (my graphics card is coming up on 3 generations behind and it still plays games adequately which would be unheard of not so long ago- if I had to guess why it would be the failure of directX10). Similarly as long as you do not feel the need to play games at 16XAA, HDR and resolutions higher than most people's monitors then you should be good with something other than the latest and greatest.
With a decent motherboard you can always whip out a graphics card and stick a new one in for minimal effort when it does start to fall behind. I have yet to see anything worth my time looking at let along considered for production in the graphics card audio encoding/filtering side of things (graphics cards have lately been opened up as high performance processors) so avoid being drawn in by anything there.
CPU: something multicore is a must and I dare say audio is up there with video in being one of the few things that benefits from having more than two cores (most of the time we suggest people stick with a cheaper/faster dual core). If you try to wind down the price a bit make sure you still have some cache as a lot of the problems can come from lack of cache when in the multimedia world where it would not have much effect on games (what a lot of people around here build high end machines for).
RAM: 2 gigs is a must if you want something slightly higher end but there is no need to go outrageous. Timings; keep the tight but do not spring for anything with a larger price tag just to shave off a cycle or two from the timings.
Size above 2 gigs; if you must go higher than go for 4 (if only for future proofing; 2 is enough for me and I do not run a machine with a pagefile/swap space), absolutely no need to go for 8 in this sort of build.
Motherboard: Get a good one, no need for SLI/crossfire compatibility.
Extra cooling: most stock stuff will be OK as long as you do not want to venture into overclocking realms. It is also €30 better spent on other things.
Case: tough one, your old machine might just be able to still be used but if not remember these can eat a good chunk of your budget (especially if you look at a fancy LED lit one).
PSU: a good power supply is a must. Most of the case bundled ones are not good and I would say 500-550W at a bare minimum.
I am going to suggest you hand this over to the local shop to decide upon and I will slice €80 from the budget to account for it, you might want €100 though. A case is a case until you are deciding that air is not longer a good thing to cool with so pick a pretty one if you want, make sure it is ATX though (you do not want to find you can not fit things in).
Monitor: you did not explicitly mention it so I assume you have one (they are easy enough to upgrade when the time comes anyhow).
Software: this is GBAtemp so such things I assume are free. Unless you want to go for linux then I say use XP instead as long as the drivers allow it (which they should).
Actual parts: Amazon do not have a Spanish branch as far as I know and I do not speak Spanish well enough for technical talk so I am basing this on flicking around on Amazon France (priced in Euros and I can do tech talk in French).
So €370, assuming no fancy audio right now.
Processor: Intel would be my choice still. Low end quad core seem to be quite rare but if you ask you can often find end of line stuff which would be great for this build. Still dual core like a E7600 looks to be about right. €130 or less should net you something nice, if you are running over though drop this down a bit first.
Motherboard- This is very much one of the "spend as much as you like" items.
ATX (not micro ATX or the like just ATX)
PCIe is a must (16x for graphics please)
Onboard sound is good.
Onboard graphics is not.
Socket type needs to match the processor (will probably be LGA775) and support the speed your processor runs at (likely 1066MHz for the frontside bus/FSB).
It should not matter if you have a shop to do it as they will probably have one kicking around the back but some slightly older boards may not work without a BIOS update- how can you get into the BIOS if you do not have a compatible CPU....
I would look to spend around €100 on it although a nice one may pump that up to €120. While I am trying to avoid ASUS right now their ASUS P5QL-E looks to be spot on.
Ram- 2 gigs of good memory appears to clock around €60-70 (you will see larger amounts but they will not be as good (slow) and may not be as reliable, unlike days of old you can more or less use whatever speed ram you like with a motherboard which is nice. Things to look for though are that you are getting DDR2 ram (DDR1 is older and DDR3 is still quite high end), 800MHz is nice (if you can timings of 4-4-4-12 but larger numbers are OK too) although your processor will most likely run at 1066MHz and matching them while not necessary in the slightest is nice.
Graphics- I avoided onboard and frankly you will probably not have to worry about the NVIDIA vs AMD-ATI discussion. You should be able to net a nice one for €65 or so (or you could go down to €50 and it would still work but be prepared to upgrade it in about a year and a half if you still want games). PCIe only; if it says AGP leave it alone. Pay little attention to ram size and clock speeds as it is not worth it unless you want to get into gaming in a big way.
Hard drives: go with one for now and if you can stick your old drive in the new machine for use as the secondary drive. No idea what you want here space wise so I am ignoring this, you can search for a review as well as any of us. Your board should have IDE but go with SATA if possible, 3.5 inch drives are what you want (2.5 are for laptops and small machines and are generally slower, smaller in space and more expensive for your trouble). €50 gets you a good, if slightly smaller, drive (320 gb or so).
Given what you have now just read it would probably be easier to pick out your own parts and for us to suggest alternatives.
By my calculations you have little to no money left to spend on things.