Hey Charles,
I'm a few days into the Xenos and the jury's still out. I recently swapped out of my RME card for an M-Audio Transit. For about 1/8 the cost of the RME, my cans plugged direcly into the unmodded Transit sound pretty good, although the resultant lack of volume control on Foobar was a bit frustrating. With the Xenos inserted into the chain, I feel like the sound is a bit veiled. A question of break-in? Perhaps. The tone controls are useful only in a very tight band, imo; I'd trade them for the EQ on an Ecler or Allen & Heath mixing board any day. If the amp does indeed need to burn-in, then my take is likely premature. I'll hopefully know more in the coming week. I've been brutally busy.
Cheers, bw