Ultimate headphone amp?

The Single Power units can be tailored just by changing tubes. If you want lush..throw in lush tubes. The 6sn7 should give you what you crave.Or try some of Mikhail's tube inserts and experiment with many different types of tubes. You have to ask yourself. Do you want a head-amp that is versatile in sound. Or one that sounds the same no matter what you throw in the sockets. I like my head-amp so much I use it as a preamp. It's the quietest tube component I've experienced personally at home..no hum, no hiss, no snaps, crackles or pops. These units are terrific tubed preamps by the way. Definitely one of the best kept secrets in audio.

Good luck with the hunt

Musical Fidelity X-Can V3 would be a good consideration. Very nice synergy w/ Sennheisers. Upgraded power supply is a definite plus.

Cary 300 sei integrated has an hp jack and cut-out switch for speaker outs so you can use it to drive your entire system if need be. The 6SN7s and 300bs give you lots of rollling options.