Which Headphone Amp for Sennheiser 600?

I want to buy a used headphone amp to drive the 600, any suggestions?
I'm using a Musical Fidelity X-Cans II on mine and it sounds great, just make sure that you upgrade the tubes.I used to only used them on my SF Line 2SE but a seperate amp really does make a difference.
But if you really want a great headphone amp check out the top of the line from Headroom.
I am also using the X-CANSv2 with my 600's. Can you explain to me about upgrading the tubes in the X-CANS?
Grado RA-1 with my Senn 600's, sounds terrific. I like the performance, simplicity, appearence, and the fact it runs off 9V batteries, one less thing to plug in.
I have a Wheatfield HA-2 for sale with a wide variety of upgrade tubes available. It's the top of the line tube amp that Headroom sells. Plenty of power for the HD600s (which I use too) and an extremely dynamic amp. If interested, contact me.
Hi Mcne, on the X-cans II, just replaced the two tubes inside to your choice of 6dj8,6922 or 7308 NOS tubes of your choice.I prefered Amperex 7308 on mine.If you have questions on how to actually open it and replaced the tubes just email me.
The Audio Advancements Earmax or Earmax Pro is great with the the 600's. I have tried the others listed here(with the exception of the wheatfield) and IMO the Earmax is a step up. You can find them used here or on E-bay from time to time for around $300.
Now I use the headphone output of my SF Line 2, but for 2-3 years I used a Headroom Supreme which sounds great. A big advantage of the Supreme is that it is small and built for travel, ie you can get an outboard 4 "C" cell battery box for longer play time, an AC adaptor, and it also has a built in AA battery chamber. Other travel oriented accessories are available.

And it can be plugged into a pre-amp via the tape output terminal either with or without a "splitter". I've used the Supreme with both Senn, 580 and 600s. Cheers. Craig
Finally found an RCA-plug/phono-jack adaptor cable at the Shack ($4) that enables me to run my new HD600s directly off my Aleph P. Sounds great!
Thanks Rmml. It is easy to open up. I just didn't know which tubes to upgrade to. Thank you.