I would look for a keyboard that has the voices you like, and use a PC sequencer for recording, editing, and playback. I use Sonar but there are many alternatives available. I only edit files using the sequencer onboard my PSR2k when "in the field" and even then only for track remix/revoice purposes.

You can easily configure your PC and keyboard so that the PC records your playing and uses the keyboard to play back the music.

You could play back wav files on the PC triggering from the keyboard (or previously recorded playing) using a PC sequencer package that included sample playback; this is not an area I have personally explored.