"So I plugged it into my computer through USB and selected it as a USB DAC tethering the jack to an old beater set of cans that I set up in my file cabinet."  I thought the X1 didn't have usb DAC capability or did they add after launch?

No you are right... I need to clean that up. My notes said I plugged into laptop and played overnight. But music playback was through the X1. It doesn't work as a USB DAC. When you plug it into the computer, computer only sees it as a storage device. I had it plugged into a constant power USB port so it could run all day and night without the battery dying.

Interesting review. I like a lot of the music you listen to, but I do recommend getting some audiophile tracks. The references to the loudness preset on the iPod and listening to loudness war tracks will induce some groans in your readership. 
 
I'd also count USB external DAC capability as a huge plus. Like Uberclocked, I wasn't aware that the X1 had it. It must be a recent firmware upgrade if it does. You won't find that in a DAP anywhere near this price point.
 
You've got some very high end gear. You should feed it high end music. You also didn't say what type of files you were listening to. If you were doing a comparison to unmodified iPods this implies MP3 audio. MP3 is crap compared to lossless. Time for an upgrade, I think, especially when you have an HD800, an LCD 2, and an ALO National.
 
Many happy listenings!