Looks very stylish too!
Most of the subtleties you are describing are similar to the kind of effects I believe I can hear with the C399.
There is certainly some kind of synergy with the NAD combination that sounds better to me compared to the 1120 and my other system, the effects are relatively small though and I am certainly not very confident that I could pass a blind test under normal listening conditions.
I have also been tempted with the (apparently only me) issues I have had with C399 to simply get the M33 and hope that's the end of it.
I do like the Schiit design, simple and understated - I especially I like the look of the Tubes on the Freya+, but tubes wouldn't be good for my health, what with having fiddleitus!! Which incidentally is why I also wanted to avoid a DAC with filters!
The only time I've ever heard really obvious and tangible differences was when demoing the speakers. When it comes to DAC's, amps, and now playing around with separate pre/power amps vs integrated. - it's all been rather subtle at best. And with most of these situations yeah I'll admit I'm not confident I'd be passing a blind test!
I don't know what I would do in your situation, clearly looking for a good sonic step up, and with my experience of speakers then I'd have to start there were I you. It's also fair to say the speakers interaction with the room too is mega important, so getting the right size and positioning is key - and at the money you're no doubt going to need to spend, that means home demos!
I'd be very tempted to find the right Ref 1 or Ref 3 deal now that the Meta's are out. I certainly wouldn't entertain the DIY route, seems like a hiding to nothing personally. I mean the likes of KEF must spend a fortune developing their own drivers like the UniQ, over decades too. And then a fortune spent on cabinet design with respect to volumes, materials, bracing, and no doubt so much more too. So the idea of just buying a full range driver and getting a carpenter to make you a box to size, sorry no disrespect the forum advocates of DIY, but well that idea doesn't resonate with me at all (no pun!).
For electronics, the M33 is certainly an interesting option, and I think given how subtle I've found electronics - that also becomes a really big argument for a single box. Especially one that has both BluOs and Dirac intergated into it too. The fact it's based on Purifi which are apparently very none-class D sounding.... well as long as NAD don't do a NAD and cripple it with buggy firmware etc then it's potentially a deal and good value too given what it consolidates.
The only draw back, no upgrading, planning, dreaming...I think I'd miss that, and the fact because it does so much, you'd feel wedded to it because replacing it would = mega bucks to be worthwhile! I bet to beat it with more traditional components you'd be talking the likes of a Michi P5+S5, Chord TT2+Mscaler, that sort of level of gear - and that's massively more money (and even then I wonder if it'll be subtle anyway - wouldn't that be depressing!).
Seeing as I'm now spending your money!
M33 + Ref 1 + 2x Micro 3000. - Feels like it'd be hard to beat that setup?!
Back to reality though, I've put the 8300A in the office setup, quite the upgrade! Replacing a little Class D Yamaha A-670. Unfortunately the Audiolab is not 'Kallax-Fi', so on top it goes!