I think the reason why there’s no CV or Gate in is because you’d need 8 of them – one for each voice of the synthesizer, right?

So, the better option, I think, is to get a MIDI upgrade on the JP-8 and, if you’re hell-bent on using the A4 to control it, that’s the way you’d have to do it. (And before anyone gripes about the cost of a MIDI upgrade, remember this is an $8,000 synth in today’s market.)

Since most monosynths of the era would have had CV/Gate in and outs (like the SH-101 someone mentioned earlier), that would be your best bet – again, if you’re looking to control it with the A4 and want to do so using CV/Gate.

If you ask me (and I realize you didn’t), there are a lot better ways to spend your money than to drop $8,000 on ONE synth. That kind of money buys lots and LOTS of usable, cool kit, vintage or new.