The current issue (July/August 2012) of The Absolute Sound magazine has a review. The review compares the two and discusses differences, plus some of the C3900DD's
evolution over the M2.
I plan on pairing my Bryston BDP-1 with a C390DD.
Here's my response in another thread about c390dd:
I am now running a NAD C390DD connected to minmac and to gs20s..Thats it..No DACs,preamps and amps..
This supposedly keeps the signal ALL digital(even through amplification) in the digital domain upto the speakers outs...
All I can say is it has been an interesting weekend..
The GS20s were awesome as usual:)
The NAD dac/amp really showed quality in its musicality..no harshness especially in the highs,though some perceive that as loss of "details".
I could just listen into the long hours without the need to keep tweaking..Lots of Tight,controlled Bass..
Listening at low volumes is just the thing I needed in my living room and NAD delivers:)
Overall happy with NAD paired to GS20s.
Minimac=>iTunes+AudirvanaPlus=>Chordette HD=> MRX 510=>Sonus faber Auditor M