Yes, me. Its excellent, it replaced a Naim 82 and all its PSUs and although I cant assess the preamp as a separate item, the overall leap in quality convinces me that adding ANY preamp after the MDAC will not "improve" the sound.
Yes, its digital, no audible degradation as long as you dont need to use massive amounts of attenuation to get a sensible level, if you do, you need to attenuate (at the power amp end of the wire) the analogue output. Ideally the MDAC should be running in the -10dB zone, but even in my relatively hi-res system I cannot hear any degradation way down in the -20s.