Maxvla pretty much captured it - that all applies to the HPA-2 as well. It's really a satisfying sound with the LM49720. Keep in mind the regular, non-USB version still comes stock with the same OPA2134. So if you aren't big on opening a case and swapping opamps (really, it's quite simple), the USB version has that added bonus for the small price difference.
EDIT btw I'm almost done messing with this loaner and then I'll get it out to you Maxvla. Should be mid week or so.
Thanks, so you say the DAC is fine? If yes, then the M-Stage USB it is.