it's possible, but not recommended as it's usually more complicated to manage, and has less compatibility.
There are three things to know:
- cIOS
- settings
- compatibility
Apparently, your issue is only the cIOS, as you managed to load wii and gamecube correctly.
but, I'll detail everything (again?) for any other users who want the info.
if you use IOS58, looking at both ports works, but playing the game won't! (this is your problem)
reloading to cIOS at game launch, if you use any non dual port compatible will lose access to Port1, don't find the game, reboot/reset to menu.
cIOS
In order to see both USB Port, you need a cIOS compatible with Port0 and Port1.
there are :
hermes cIOS (any)
cIOS d2x v9 beta (unreleased apparently?)
dIOS d2x v10-alternative (r53)
So, if you are on Wii, you can try hermes cIOS. if you already have any cIOS in the 220-224 range, these are the one!
if not, you can install d2x v10 r53 in one of your slot (251 is rarely used for example).
you could install r53 base57 in slot251 ?
set your loader's setting "Game's IOS" to use one of these slot.
set your loader's settings to either "IOS58" or the same slot than the "Game's IOS".
I'd recommend to use both the same IOS, not IOS58.
Settings
cIOS was the first step only!
Now that the cIOS is compatible with both ports, you need to tell the loader to actually look at both ports!
Settings > HDD settings > Port : Both !
And if you want, you can also have the loader list games of both ports at the same time !
settings > HDD settings > multi-partition : enabled
Note that the multi-partition option is only for Wii games.
For gamecube games, it's a little more complicated.
now, having both HDD at the same time, the partition order will be different based on the IOS you are using for "loader's IOS".
if you use a cIOS in the loader's interface (loader's IOS) then ports are mounted in incremental order (Port0 -> port1)
if you use IOS58 as "loader's IOS", they are loaded decrementally (Port1 -> port0)
The "first partition" loaded by the loader as "usb1:/" will then depend which IOS you are using!
you will need to properly set both partition of the Wii and the gamecube (and everything else, like emuNAND, covers, themes,
cheats, etc.) here :
Wii : Settings > HDD > Partition : select the partition where you want to "install" dumped discs. This is also the only partition you will list if you don't enable "multi partition" option.
Other : Settings > user path > Change every path to reflect the proper HDD partition.
usb1:/ is the first partition loaded by the loader
usb2:/ is the second partition loaded by the loader
usb3:/ the third, etc.
Compatibility
unfortunately, r53 is a beta version and has less compatibility with both hardware AND software.
Some HDD are not working at all with it.
if your HDD works, some games have issues with it ! either not working at all (black screen, like just dance) either freezing randomly while playing.
WARNING
when using dual HDD setup, NEVER use your HDD as the place to store any of the application files.
no boot.dol
no covers
no
cheats
no settings
no themes
no audio
NOTHING OTHER THAN ISO AND WBFS!
If you ever have a file loaded by the loader located on the USB while inside the Loader's interface, you'll crash the console, and you can also lose your partition data !
It's because USB are not really loaded at the same time. they are unmounted, switched, remounted.
if you have a used file (say the settings, cover, or audio steam music for your theme) on one HDD, then trying to list game from the other USB port will force the USB port to shutdown, losing access to your opened file currently steaming (audio or text is a stream), and the App will try to access/read/write the same data from the newly opened USB connection at the same place the other file was located ! it could damage your file table and content of the partition. you can lose files!
ONLY EVER USE SDCARD FOR HOMEBREW RESOURCES !
this is very very important!
for all your homebrew, always use an SD card ! this is the basis for wii homebrew. don't be cheap, SD card are not expensive at all. buy one if you don't have homebrew on SD ! put all the /apps/ folder on SD ! never on USB when using dual port.
Conclusion
it's possible. it works. badly.
it's a feature of the loader, but it's not really encouraged to use it due to r53 requirement (and incompatibility).
For game compatibility you'll probably have better chance by trying Hermes cIOS instead of d2x v10-alt ! try slot222, 223 or 224 ?