Demultiplexer where ? read the webpage and the manual - and what is inherently wrong with 'demultiplexing' (in it's variations) ?
Been a while since I played with MIDI, but what is 'real time channel' ? No delay huh? Maybe you mean to say 'delay within a spec that you define as acceptable'.
only a DAC can do the job Properly for real analog sound
Well, um - er, would have thought only an analog originated CV would do the job properly for a real 'analog' sound?
Besides it's not so much the control voltages that give the sound but the oscillators, envelopes, filters and so on, I can see that having unnecessarily quantised/bit-steppy CV won't help, but it's not the main concern. If I recall MIDI mod-wheel for instance is 8bit anyway, so what is your DAC going to do with that? It can (theoretically) smooth it (LPF), but then you've got a delay...
Once you factor in time costs the PAIA kit looks good, but then you won't have all that learning under your belt, and the ability to alter your project for your needs - up to you :)
-- Maybe my time away from synths has made me forget the details, or I never knew them properly in the first place?