Thanks for the feedback guys - it was an overly large SDL_Mixer buffer causing the sound delay. I reduced it from 4096 to 64 as recommended, and it's working great now!
There is still a bit of a problem with the high score entry - by default Powermanga expects standard key presses to enter a name, which doesn't work too well on the GP2X obviously
I created a simple mapping from the GP2X buttons to the characters A-G, so you can (sortof, very clumsily) enter a name now. I set the left dpad button to SDLK_Left instead of an alphabet character in the hopes of allowing you to back up and re-enter characters, but it doesn't seem to work.
I'm not going to try fix this as it stands - I'm rather going to try implement the standard up/down+enter letter cycle as used in arcades, which will be far more suited to a handheld. It might take some time to do however - deciphering source written in French when I don't speak a word of the language turns out to be rather tricky...
Anway, I've updated the downloads (game+source) at the file archive to include these two changes, so the game should be almost perfect at this point. I played up until level ~27 this evening without any problems, so I assume it's possible to complete the game.
Forgot about the sample rate question: All the sounds are either 11KHz or 22KHz mono, so no problems there. I originally thought that this was the cause of the problem and so checked them all, but they were fine as-is. I did however end up reencoding the music at 22KHz instead of 44KHz to see if that made a difference, but no such luck. Thankfully it was down to something as simple as a Mix_OpenAudio() parameter change
