PS Audio PWD II vs. NAD M51

Can't speak for the PS but my M51 has not only replaced my previous dac with great sound, but my highly regarded preamp as well. It is a very transparent arrangement. If you think you might want to go down the all-digital road the M51 is an amazingly good way to get there.

I have a PS Audio DS DAC on the way. Up till now my NAD M51 has easily beat the EMM CDSA SE (an $11,500 dud), the AMR DP-77 (complete with tube-rolling failures), the Antelope Zodiac Gold, and the Berkeley 1, among others.

The DS DAC just retired my beloved NAD M51.

I have both. They both sound great and would be happy with either one, but if I had to choose keeping one, I prefer the PS Audio DACII over the NADM51. The DACII has a bit more air, warmth and musicality. 

The M51 is a great DAC,   I love mine , but I think they are about to retire it soon.  There have been no firmware updates in quite a while.  I have no plans to replace it anytime soon it's that good.  Good deals on used ones.