Funny how tastes and impressions differ. I own the original Auditor for some time now, I've tried different tube and ss amps, CDPs, interconnects and speaker cables. I never found them overly warm and laid back, quite the contrary, they provide an amazing presence and liveliness. In fact they even exaggerate a little in the higher mids that, depending on the recording, can add a slight harshness when played loud. You need to choose your amp, source and cabling *very* carefully in order to minimize this. If paired blindly with whatever electronics you will most probably end up with a fatigue problem or, in some cases, a dead and dull sound.
From what I read the new M version does not have that problem but sounds more hifi like instead. More air, more detail, more of that crystal clear sound many peolple like. That's reason enough for me to believe I prefer the original Auditors. Happy me, because I couldn't afford an upgrade anyway.
I've ended up with a Luxman L-505f, Meridian G08, Yter XLR ic and Van den Hul CS-122 speaker cable and the result is 98% perfect. The logical speaker upgrade would be a pair of Guarneri Mementos, not the Auditor M. Electronics that were the worst match of what I've tried: Electrocompaniet ECI-3 integrated, AudioNet ART G2 CDP, Kimber 4TC speaker cable.
Anybody who wonders which one to buy, the original Auditor or the Auditor M and does not have a chance to audition them both, keep in mind the following: It's easier to build a great system around the new Ms but the original Auditors might reward you with more emotion. If you succeed to find the matching electronics for your listening room. And that will take time and money.