There was a MIDI version of the Poly 61 called the Poly 61M as well as a retrofit from Korg. Both are long discontinued. I have seen Poly 61 MIDI retrofits in the back of Keyboard Magazine. The synth doesn't respond to velocity or aftertouch and adding MIDI won't help. I wouldn't sell it because keeping some of those wanky sounds around is worth more than the price it would fetch. Good luck!