Only wav is supported but the Sonic CD in Sonic Gems Collection is the PC version, which is better in my opinion, the fmv intro and endings have better quality, it's lag free, it just performs better than playing it on a Sega CD or Genplus GXI only got 1.7.1, I didn't know they made an update, I got the game as iso+mp3+cue does it support that?
I don't see why Crediar can't fix such a simple thing, he's probably not aware of it.
After all it was WiiPower who fixed it with disc-inserted, how hard can it be to apply it to no-disc?