Just catching up on this thread - great discussion up above about tube amps that pair well with the LCD-X. Very interesting stuff.
Personally, I've heard the LCD-X driven by the Ragnarok, WA5, Cavalli LAu, Mjolnir, Asgard2 and Bryston BHA-1. IMO, the X sound decent with all these amps.
I think the bigger factor in making a good rig with the LCD-X is the DAC. It controls the SQ of the music that you hear. The amp just colors (a bit) the analogue signal that's sent to the HP's. The X are so easy to drive that the amp just kinda gets in the way, IMO. Feed a decently-decoded signal to your amp and LCD-X, and you won't be disappointed.
BTW, I think that Schiit Audio's idea to make the Mjolnir a SS/tube amp was one of their best decisions ever. This amp allows for pure SS sound or tube rolling. You don't have to go all the way to Woo Audio to roll tubes, although the Woo amps are certainly sublime.
This from an LCD-X owner since 2013.
FWIW,
RCB