Figaro gave a pretty big nod to the EF-6. I'm betting it would be good for my other phones, too, but it's a bit too expensive for me at the moment.
Mjolnir might be an option. I don't have a balanced source, but it has RCA's. The only problem is that I wouldn't be able to run it with either my HD600 or HE500 as I don't have balanced cables for them.
Dan, were you speaking of the Soloist or the Phonitor?