If you just want to control MIDI device, you can do everything with a single PIC. Now if you want to produce Noise, Sound, Instruments... that's another story. If it's just simple tones... no problem SOUND, HPWM could work in some range of frequency. For the others.. a simple High/Pause(us)/LOW/Pause(US) loop will work.

MIDI protocol is pretty simple and highely documented all around the web. Few minutes on Google will give you tons of links.