Still loving the '65 Gemini I you sold me!
These old Ampegs are famous for their reverb and tremolo but this amp takes them to another level. The verb is speaker driven...the output of one amp feeds the reverb circuit which sends the verb to the other amp and the trem has this phasey thing going on between the channels. You can play through just one amp or both.
What I do is on some jazz gigs is run my Strat though an overdrive pedal into channel two and thus one 15 watt amp for some bluesy grind and my 330 or 175 into channel one for 30 watts of warm, clean, gorgeous jazz box tone for the straight ahead stuff. I leave both guitars plugged in and just pick up the appropriate axe for the tune.
It takes pedals well and has a unique octal tube-Ampeg-cathode bias-7891 clean tone that drips with mojo.
Speaker driven reverb? Never heard of such a thing, but if it's better than the reverb in some of those other Ampegs you've got listed, I could see why you love it so much!