Thanks for your reply. I have a couple more questions.
1) My Sysnand is delinked. What exactly are the consequences of making a new emunand from this (and using it)?
2) I can't even see the band partition on my Mac. Therefore can't see the size of the nand. What should I do?
Emunand is literally a clone of sysNand, but stored on the SD. That's all it is. Linked NANDs means that your ticket is the same, and that you can use the same software/saves on each of them.
In a 3-NAND set up (sysNand and 2 emunands), all three can be linked if you don't format any of them. Which will allow easy transfer between the 2 emunands.
So to answer your questions:
1. Your new emunand would only work with your sysnand stuff, and any new emunand stuff. The old emunand would be incompatible. If you want your old emunand stuff, you gotta extract/import the emunand as I mentioned above. That is: make new emunand based on your sysnand -> extract old emunand -> extract new dummy.bin -> combine and write to new SD. That would give you your old emunand on your new card.
2. Right. As I said, Mac doesn't support this specific type of format, which is a bit of a problem. Did you back up your sysnand? You can do this by booting the gateway go exploit (and I think MT's launcher can as well), and selecting "back up NAND". This will put a NAND.bin on your SD card (on the file partition). Just look at this file's size. Using right click -> get info. And compare with the listed sizes on the page I linked. Your emunand will be the same size, so you don't need to worry about that.
So all in all, here's what you want to do:
1. Back up sysnand using the gateway go (web browser) launcher. It's literally called "back up NAND" or something of the sort.
2. Look at the created NAND.bin size to determine toshiba/samsung.
3. Put in your old SD card, and extract the Nand using the method mentioned. Ignore the dummy.bin line.
4. Put in your new SD card, and extract the dummy.bin using the method mentioned. Ignore the NAND.bin lines this time.
5. Run the lines to create the SD_tmp.bin using the extracted new dummy.bin and the extracted old NAND.bin.
6. Write the SD_tmp.bin file to your new SD card.
7. Transfer your stuff from your old SD card to the new one.
Keep in mind, that you might get a "resource busy" warning. If this happens, unmount the SD card using "diskutil unmountDISK [diskname]".
Step 3 extracts your old emunand, step 4 extracts the partition info from your new emunand, step 5 combines them, and step 6 writes your old emunand to your new card.
Hopefully that clears things up. If you transfer your old emunand, then it will function exactly as it does now, just on the new card. You can, if you'd like, keep the old card with the old emunand (don't erase it afterwards), and run 2 emunand SD cards, swapping them out as you please. A similar setup is used for CFW.
Edit: When transferring the emunand, make sure you did "format emunand" on your new card, so that there is indeed an emunand partition. Otherwise it'd be unreadable garbage, haha.