Grace Design is now shipping the M900!! It's the same as the MassDrop M9xx except that it adds a coaxial digital input. Price is the same, $499.99. You can order it in a few days from retailers listed on the Grace Design website.
I have the high-end Grace Design M920; I also have two NuForce DAC-80s; as a Dac/Pre, I prefer the sound of the NuForce unit! The M920 has a load of Pro-audio features you probably don't need. For studio work, the M920 feature set is invaluable. The DAC-80 costs about 20% of the M920.
Do your due diligent research, then decide. See also "khaja-724612" below!