As I said, I'm not able to listen to it right now and I'm afraid it will take quite some time for my amp to return. I noticed strong static noise on the left channel of my Emotiva A-100 (Emotiva kinda being infamous for shoddy QA), so I had to send it to the reseller, who - in the worst case - will send it to Emotiva in the US, who will take some time to repair it and then send it back to Germany. I'm still expecting it to take a few weeks from today. Others will long have made their review by then! I'm listening on an SMSL M3 right now and the M400 (and the D90 before) was ment to be my shortcut to endgame in the DAC department.
I can only help you with the points that made me prefer the M400 over the D90: I prefer the optics and the format fits a tiny little bit better on top of my amp. I didn't like the white on black display of the D90 much, but the color display of the M400 is more of a gimmick, if you ask me. Despite me planning to mostly use the M400 as DAC-only, I do prefer a knob over the D90's buttons. You never know what use you will make of a device in the future. I was expecting the measurements to best the D90, which it kinda achieved, going by Wolf's measurement. The IMD hump is negligible it seems, and tbh I don't even really understand what that is.
Btw. shouldn't that be an ESS issue, not AK?!
I'm an IT guy, not an electric engineer. That said I do appreciate measurments and somebody pointing out that the one is better than the other.
About MQA: I've read so many statements for and against it that I decided "F#ck it, I'll check it out myself!". Actually before deciding to check out MQA, I was also looking at the Soncoz SGD-1. If you're not after MQA, you should check that out as well!