DAC choices? Musical Paradise, Metrum Octave?

Hello everyone-
I'm wanting to purchase a new DAC for $700 or under (okay with used) and would prefer to stick with USB connection. 
Wanting something more resolving than current MusicHall 15.2, and really groove on detail, soundstage, and a bit of warmth. 
Set-up is:
Parasound A23 amp
Consonance Cyber 222 tube pre
Gallo Strada speakers & M&K sub
Macbook Pro

Has anyone heard both the MP-D1 and the Metrum Octave? I know I'd need SPDIF converter if I got Mk 1 version of Octave, and I've heard good things. But tempted to go with MP because I love tube sound. Suggestions?
Other recommendations? 
Thanks!
Linc