cool sounds!
is that a feedback pot you've added to your 64?
I've got mssiah - which is very cool. I've made a breakout box for controlling it but not tried feedback pots yet.
-and electoyd I think you mighht be thinking of Synthcart for atar 2600? If you do get that running with yr midi retrofit post some sounds please!
I think there's some prob sythcart and with uk PAL tv's though?