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 big picture in the centre of this site:

http://ipodstudio.com/index.php

shows a Larocco amplifier which was designed to use with HD 650s. It's off PPA design.

Click on the picture for more pics and details.
Ive used my rkv with my hd600s for four years now, sounds fantastic but I cant compare to anything else as I havent heard any other amps. Ive never felt on the other hand that anything was wrong so never thought about upgrading. Its worked wihout fault for four years but I think I should look for some new tubes for a possible upgrade.
I bought an RKV secondhand a few months ago, no problems to date. Remarkably immune to tuberolling. Seems like a sturdy piece of equipment to me.

Patrick