Interesting results...I went back to the upsampling and re-tried the X4 upsampling setting. I'm not sure if this was the expected result, but I really started to notice on X1 (no upsampling), the vocals were very upfront and fatiguing (lesser so on non-vocal music, but still not quite ideal). Doing some more critical listening, the X4 setting really seemed to move everything back. On both the Lyr and the A8C amp, the brightness of the HD800 was still present but lost a lot of the fatigue because of the loss of the forwardness of the sound. I actually wanted to turn the volume up on a couple songs, which is a rarity for the HD800. I was *gasp* having fun with them!
So now I am wondering if the forwardness of the X1 setting lends itself well to headphones with more recessed mids, such as the TH900, as it is said to be a great match for the amp. It's too much for me on the HD600 and HD800, as both headphones are way more enjoyable with the X4 setting.
I am renting a TH900 from the Cable Company, so hoping for the best.