I dont know if anyone here has this DAC, but Stereo Net Australia board member lil Caeser seems to have heard most of the current ~$1K front-runners and rates the M51 very highly:
Just ignore that stuff about the Lampizator unless you happen to have 5K ......
NAD Product Page - http://nadelectronics.com/products/masters-series/M51-Direct-Digital-DAC
NADs Youtube vid:
Sadly, the only other review atm seems to be in Dutch - NAD have kindly translated the highlights : http://nadelectronics.com/articles/HiFidelity-Review-M51-Direct-Digital-DAC
(Google Translate, IME, turns reviews to something resembling the rantings of a madman - YMMV)
I look forward to those impressions for anyone with $1500.