I’ll try—I have an Analog Keys now since selling the A4 some time ago. The Keys has the level of expression I wanted out of the A4 + QN pairing; it’s keybed with aftertouch plus mod/breath/pitch joystick works really well.
When I did run the A4 + QN, the MIDI Expander simply connected to the A4 via MIDI DIN, as you’d expect. I didn’t have to do anything with the QN itself in terms of setup. Overall, when I first got the QuNexus I did mess around with some of its settings using the app on my Mac. Primarily the touch sensitivity settings—the default curve was not giving me a pleasing range of input. It felt too quick to ramp between my typical playing pressure and WHOA FULL Values. I tweaked the curve to suit my playing style, which made it much easier to get more nuanced expression from the A4, e.g. Modulation from 0 - 64 on any given patch.
Ultimately, the Keys was just more immediate, more aligned to actual performance needs. I haven’t used the QN for anything since, expect perhaps for some rare, just-for-fun noodling on an iPad synth app.