Best headphone amp for new Senn 650's


I just ordered a pair of the 650's with an upgraded cable from Drew at Moon Audio. I have been over at head-fi.org and Headroom Corp. and looked through these forums too and have come up with several possibilities for a new headphone amp. My question is, is there something that would considerably improve upon the Antique Sound Labs MG Head (older version with transformer, and Telefunkens) that I currently use with my Senn 600's? I am tempted by the Headroom new Max, the Grace 901, the Sugden Headmaster, and various other esoteric things I read about at head-fi. There are a lot of headphone listeners here, too. Any thoughts on whether I could substantially improve on the MG Head? Maybe other tubes than the Telefunkens I now use?
sc53
The best? If you like tubes, then the best is a Cary 300sei (a lot of bucks!). Now, this is true for me; to my ears. Next best? Earmax Pro.

The Grace sounds fine but it is definitely solid state. The internal dac is not a very good one (sound-wise). The very high end HR Max stuff does sound very good (better than the grace) but also sounds solid state and costs way too much money. Just my two cents.
The Cary CAD300SEI is a killer headphone amp... definitely overkill on the high end of the scale $-wise, but excellent sounding. it and Senn 600s Kicked the butt of a Stax set up I had on audition for a while. Doubles as a great little integrated for small to medium room systems with speakers of 87db/1wm sensitivity or better. Add a CD player and it's a two-box system.

-Ed
If you like tubes, try the Earmax Pro. I've been very satisfied with my Pro/Senn 600s. The tube combination I've found to my liking is Telefunken 12AT7 and Bugle Boy 6DJ8's. I could listen for hours (and do)!
Just my $.02 here, but since you didn't limit the price, I agree with Ed and Jim that the Cary SEI is nice. I disagree that the Earmax is next best though. I had the Earmax and it was (in my tastes and in my system) not any better that the headphone jack on my Pioner Elite CD recorder. I also have a Headroom Cosmic which easily bested the Earmax. My main headphone rig, like the Cary SEI, doubles as a very nice SET integrated - the Moth Audio SI-2A3. If you like a typical warmer but clean and detailed SET tube sound, the Moth is fabulous. If you like a little more slam then the Cosmic has more of a solid state sound and is tighter in the bass with nice dynamics.

I also had the first version of the ASL MG-Head amp and, although I liked the sound, it cannot drive the Senns to any decent volume and the Moth is much more dynamic, with better detail and focus.