I am running my X1/Grand Slamms with Gryphon Class A amplification. I have heard these with ARC Tubes and heard the Alexandria with Krell Evo Ones. I prefer the sound i have to both, and would not trade it for tubes that i have heard to date despite being extraordinarily tempted by the Lamm 2.2 monos at one time. I might be tempted by CJ ART, but with the Gryphon Colosseum, i have not even bothered to inquire.
As Steve says, its a personal decision at this level of quality. It also matters what else is part of the system.