Not sure if this topic is still relevant, but I had a similar issue on the Wii port of ScummVM, also using MP3 tracks stored on SD card. The Ogg format apparently improves the seek time.

As an Omnia owner myself, I'll be keeping tabs on a 240x400-supported build of ScummVM. Not getting the fullest out of the screen makes the ScummVM experience rather weak. On a different note, I saw the scummmodern.zip file with what appears to be an xml-based skin. I tinkered around with it a bit, ...