Bit of advice for others. If you're struggling to find the bios or run games, update your assets on the Retroarch menu. Once I did this, the entire menu structure changed to a nice icon one, and all the bios files seemes to be found aautomatically.
Onto the games:
Resident Evil 2 on gamecube was a black screen, but had RE noises responding to my button presses.
A LOT of PS1 games just refused to run for me. A damn shame I couldn't get Die Hard Trilogy 1 or 2 to run, nor Dino Crisis 2. I kept trying each of the PS1 bios's had (rearmed, duckststation, beetle, beetle + hw). Quite disheartening.
How can one pull up an in-game overlay menu, you know for editing the resolution/visual settings? Some PS1 games that I did get working look horribly pixelated on my TV, for example.
Also, is there a way to exit the rom that's running without having to go to main XB dashbaord, quit Retroarch retail, then go back in and select a new game?