I think you are confusing the memory for Voice expansion with the memory for multipad .WAV's.

The multipad audio is read directly from the USB stick, I believe... Whether there is an upper limit, I am not sure, but 16bit/44.1k uses 10.1 mb per minute or 30.3 mb per 3 minute song, so even if it WAS a 64MB limit, that's about six MINUTES of loops!

Not too shabby.