The issue with the NAD M22 is that it is a switching amplifier. So even though it might have a lower noise floor and more power than the C275, the amplifier probably switches at around 500kHz whereas DAVE first upsamples to 705/768kHz and then further upsamples to 104MHz with noise shaping to get you great timing accuracy and remarkable transients. So I personally would strongly advise you against getting any Class D amplifiers as an upgrade from the C275.
I own the Chord Etude so I'm biased but I really like it. Another amp I like that I found superbly transparent is Bryston 4B3 although I think I still prefer the Chord Etude slightly more. Part of the challenge in getting a good Class A/AB amplifier to pair with the DAVE is that many excellent amplifiers are still not as transparent as the DAVE (which is probably why you're already thinking about upgrading the NAD C275 even though it's already an excellent amp). And as I said, class D amplifiers that are transparent and dynamic ruin the transient accuracy of DAVE. So if I were you, I would enjoy the DAVE with the NAD C275 for a bit longer for now and start slowly exploring what amplifier you want to upgrade to. (btw, I presume you're hooking the DAVE up directly to the C275 as I have yet to hear a preamp that's truly transparent to the DAVE. Although I know some people in the forum/thread disagree).