When you want to do electronic music editing and still have ability to play it in using real instruments – MIDi interface is great choice. Not all instruments have MIDi interface, so instead of looking for commercial solution, why not to try build one by yourself. Spic0m have put together a small PIC16C84 based circuit that picks drum signals and transmits them over MIDI.
Input is made very simple – piezo transducers on port pins RB0 through RB7. Software simply transmits equivalent note to get required drum sound. Due to its simplicity there are few limitations like fixed channels, fixed volume and of course the need sound module which would synthesize drum sounds. Either way a PC software can deal with all those problems. If you need different parameters, you can make changes to firmware.