Did you ever consider the Alpha Dog? Great isolation, terrific value and far more comfortable and less picky with regard to amping than the XC. The Audeze is technically better but it's not always fun - even with the volume cranked up. By the way, is the top of your head made of granite and do you have a strong neck? Just saying, they're superb headphones but I would advise anybody looking to buy to take them for an extended demo before making the purchase. They're not for everyone. They're very energetic in the upper mid and treble regions too. Something to think about if you suffer from tinnitus :-)
Neck is strong. Head of granite? Depends on who you ask.
I've got the LCD-3 (Fazor) and never had a problem with the weight or comfort--I actually find them to be pretty nice to wear. So, I don't think the XC is going to be an issue--especially since I'll usually be laying down while listening to them. I think that clamping will actually make it easier to keep them in place when my head is on a pillow. That was an issue with the TH900--too loosy-goosy when my head was on a pillow. VERY comfortable when upright but not good for use in bed.
As for the AD, I've not really considered them...don't know why...probably should have...but...too late.
Problem is, I'm rather sick in the head and I just ordered a pair of XC's at what I consider to be a tough deal to pass on... So, this is kind of a moot point right now. I'm hoping I'll like them. A like-new set of TH900 will likely be up in the for-sale section pretty soon! :-)
Regardless, thanks for the input!