You have two solution when a game have a multi-game menu:
Solution 1: Choose the game to play before booting
Go to USBLoader GX > Game settings > Alternative dol :
- Select on boot (it will show you a list of possible sub-game when you launch it).
or
- Select Dol + Select Dol Offset (it will allow you to select the dol manually once by clicking on the line just bellow from the "Select Dol offset" option). This time, it will not ask on boot, but always launch this selected dol.
Advantage: quick boot the sub-game
Disadvantage: no menu, save management, etc. if these are selected from the main boot.dol (like for Metroid prime)
Solution 2: Allow the game to reload the IOS
- You need a recent USBloaderGX version (2.3+ I think)
- You need to install d2x cIOS (I think v4+ or v6+ I don't remember). just install the latest v8
- Go to USB Loader GX > game setting > Block IOS reload : set to "ON" ("Auto" should work too if it detects d2x, but set it to ON to be sure)
- be sure that the game is using the IOS slot where you have the d2x installed.
that's all.
Launch the game, it will play like it's intended and you can select subgame without the Wii reseting.
Usually, when a game has multiple dols, the loader says "communicate this value to the development team".
You saw that message?
if yes, which value did it gave you?