hi ron, firstly you need to purchase the MP3 board which is pretty simple to install...the only way to use the processor would be to somehow seperate the vocal onto a seperate track and route this into the processor line in,from prob the out 1 or 2 jacks (as these are dry independent outs) and then have it come back out the normal l/r main outs of the korg..i have used the vocal processor on occasions as outboard EFX for the bands vocals, on certain songs, but that was in a live situation, not with either midis or mp3's...it really gets down to how well you can seperate your vocal track, and if you REALLY want to bother!! although another ,method just popped into mind...as the pa has a dual sequencer, you could run a seperate mp3 thru sequencer 2 which just has the vocals and blend that with the main song mp3 thru sequencer 1???
though i dont know if all this would be really practical or would even work in practice...just some thoughts though
cya
dennis