I received mine yesterday. I never heard the Mk-I in my system so I cannot address that comparison. I can say this, right out of the box with NO warm-up I have mixed feelings. My former reference was the Sonic Frontiers Transport 3 and Processor 3. This VERY early impression (which, to me, means nothing but you asked about "right out of the box" impressions) are first, that it lives up to its wonderful analog sounding reputation (this thing is less "digital" sounding than the T3/P3). Second, however, it is less detailed than the T3/P3 and, RIGHT NOW at least, its bass impact and defintion are much less impressive than the T3/P3. I fully expect this to change from all that I have heard about how it changes after burn-in.
I am running it 24/7 and have David Elrod's EPS-2 power cord on it so I expect it will be impressing me MUCH more very soon. I will write more when it really has had a chance to stut its stuff.
Again, THIS IS A RIGHT OUT OF THE BOX IMPRESSION SO TAKE IT AS ONLY THAT AND NOTHING ELSE.