That's the thing, the LCD's will scale up with better gear. The Lyr at $450 is a very attractive starter amp with them, but if you're dumping a couple hundred more into tube rolling I'd just assume moving into a better amp at that point. Put a pair of HD800s on the lyr and those reveal every little limitation of the amp, the LCD2s kind of smooth it out and make it pleasant.
I've also listened to the LCD-X and LCD-3's on the lyr with orange globes and I couldn't hear too much between the LCD2s and the LCD-X's which I believe was a limitation of the amp. Once I moved these over to the GSX and master 8, there was a clear difference between them. The LCD 3's were the best of the audeze's on the lyr to my ears, the mids were so nice and there was a lot more air between the instruments but cost of admission is really getting up there.
They LCD-3s get quite a bit better too. While I loved the LCD-2s on the Lyr, I was astounded that the synergy didn't follow to the LCD-3s.