I also have Merlin Milleniums with battery bam. They're currently powered by a Berning 270. It's clearly superior to my other amp (Mesa Baron) in some ways--detail and resolution, better bass contol, for example. On the other hand, I had it at my local high-end dealers, where he had it in his system with a Wadia 861 and Vandersteen 5's. He didn't really like it, but then he's a hard core audio research fan. He did say that in his opinion, it was noticeably faster than the VT100 he had there, but he didn't like the midrange. Synergy is the key word, I think.
There are practical concerns as well. The Berning weighs 10 pounds. I can put my hand on the grille without my skin burning off. The Berning has built in power conditioning. I'm sure you know all of this, but these things are worth considering.
Finally, search archives here and on Audio Asylum. There was some discussion a few months ago about the merits of transcendent, atma-sphere, etc. For what it's worth, one guy definitely preferred the Berning over the 25 watt stereo Transcendent.