I wouldn't think my PPA would trick a tube head into thinking it was tubes, but maybe it's the OPA627's as it lacks a lot of that solid state twang. Jason's did have the 8610's in L+R, which again may be excellent in thier own regard but are quite ruthless and well open in the treble.
One quick comment on the bass with the Perreaux - I'm talking more with the HD650's. With low Z cans it rocked in the bass region but felt lighter to me with the HD650. Not the case with the PPA.
With bass boost on, the bass would satisfy anybody who demanded a healthy dose of bass! I tend to leave it off but last night I had it on most of the night and it rocks the HD650's big time! Oh, and Mark tweaked my bass boost as it had a .1 cap if I remember right the first time I had the amp and the bass boost was waaaaaaaaay overblown. Not so much in dB's but in it's breadth of boost. It went way up into the midrange and made it sound like a loudness filter had been activated. I don't know if that is the standard cap size that the build specs call for but you guys waiting for an amp might inquire about this. I think Mark ended up with a .22 or higher cap, which makes the roll off much steeper. After Mark tweaked mine it's perfect.
xtreme4099 - Thanks for the opamp impressions! I intend to experiment some one day, but very happy right now. Again, I have a penchant for a more forgiving, maybe a hair darker sound myself. I'm one of those people who have gone back and forth between tubes and solid state over the years with headphone and two channel gear.