alright guys, enough talking about microdac or stello and back to the topic of usb vs optical/coax-in on the mhdt lab dacs. well, i don't have the constantine, but i was able to compare the usb-in with the optical-in on my paradisea+ for a couple hours today. i believe the paradisea+ uses the same usb chip from c-media as the constantine. to me whatever difference between the two inputs was very very small. i think i hear a little more treble sparkle and high-frequency details with the optical-in, on the other hand, the midrange of the usb-in seems slightly fuller sounding. it really required some careful listening to be able to pick out the differences. if i was blindfolded, i highly doubt that i would be able to pick out which one was which. forgot to mention, my source was itune playing apple lossless files through my computer's usb port and built-in optical port (realtek). anyway, i definitely didn't find the drastic difference the original poster found in his constantine. going into the comparison, i was totally expecting to hear a much worse sound from the usb-in, but that was not the case. on a side note, the improvement i heard when i upgraded the power cord and when i put in the bendix 6385 tube were significant greater. just want to share my finding...