Its interesting you say that because many folks in this thread sing the praises of the Mjolnir Gungnir combination with the XC.
One person's detail is another person's unlistenable. One person's neutral is another person's analytical. Different strokes for different folks. That's the beauty of it. Nobody has to be wrong!
Communities like Head-Fi and internet reviews are great. Those folks are the main reason why I even tried it instead of going with something more familiar. These things make site-unseen direct from manufacturer purchases and Schiit's entire business model possible. However, when push comes to shove, I trust my own ears over anonymous internet posters when it comes down to the final decision of what stays and what goes.
It really seemed incredible for the first few days, and then I left for the weekend, my extension 4pin cable came in from Blue Jeans, and now everything seems different. It's like I have my w5000's again, everything seems kind of grating and painful like the highs are too high so I can't listen to the music as loud as a I used to.
Your experience sounds VERY similar to mine. At some point I plan on trying to do a more complete writeup of all my new toys, but I catalogued my problem in an LCD-3 thread here:
http://www.head-fi.org/t/588429/audeze-lcd-3-appreciation-thread/2595#post_10480146
I don't know what you listen to, but I can give you one clear example of where I thought the Gungnir didn't work well for me.
On the opening track of Alison Krauss & Union Station's "So Long So Wrong", there's a little intro bit with banjo before the main vocalist starts singing. Once the singing starts, it's overlaid with the banjo. With the Gungnir, I found the plucking to be hyper-detailed/edgy/accentuated, and once the singing started every time the banjo played it was more forward than the vocalist, almost drowning her out. With the other sources I tried (Violectric V800/Arcam CD72), the vocalist was still the primary focus. To me, the difference on this track is night/day.
I experienced listener fatigue with the Mjolnir/Gungnir combo almost immediately, but I kept thinking it was something else like the Mjolnir's dynamics and the ridiculous range of "loudness" when switching from classical recordings like unacompanied cello to modern pop. It took me the full trial period to find a single track where I could find a track that demonstrated the main problem so easily and convinced me that it wasn't just my inability to manually control a volume dial.
Same problem was exhibited when using Gungnir/Violectric V200. I think I tried Gungnir/Beyerdynamic A1 and had it too, but now I can't remember. Same problem was NOT there when using V800/Mjolnir or with Gungnir/V200/(Beyerdynamic DT770 600 Ohm/Sennheiser 595). For all I know, my particular LCD-3, LCD-XC, and Gungnir were a bit bright in the same region as a sensitive part of my hearing. Source material/quality also changes a lot from person to person and even from track to track. As always, YMMV.
If you haven't already done so, try it again without the extension. I'd be willing to bet the differences are related to the enjoyment factor of new gear vs the introduction of the cable. In my experience, the best way to demo new gear is to do the comparison over days if not weeks. Listen to the entire spectrum of music that you like and then listen to the same things again in the same order on the other set of equipment. If things still strike you as good or bad after that time, it's a pretty safe bet that your brain is fully dialed into the sound that you're getting and that's what your reaction is going to be long term.
P.S. I don't want to get into a huge cable discussion, but IMO Blue Jeans seems to make pretty high quality stuff in terms of solid construction and good parts (I own an HDMI cable). I went with custom-made Mogami cables from proaudiola almost entirely based on price difference from BJC. Outside of non-standard cable designs, I've generally found differences to be in the range of subtle to non-existent vs game changing. Given the reportedly the non-reactive load of the LCD-XC, it shouldn't be a complex headphone to drive either.
