I've heard both, and you're getting at that level where it's not so much that one is better than the other, so much as which one aligns with your tastes more. They're not very different -- I mean, c'mon, they're both "best ever" type amps -- but there might be subtle differences between the two, especially with multiple electrostatics, that might make you prefer one or the other with a certain pair of earspeakers. You should wait until you get it and then decide.
It's really good -- you should at least hear it.