I've spent hours reading this thread and haven't really learned too much. Most of this stuff is way over my head. Three days ago if someone had mentioned "tube rolling" I would have guessed they were talking about some new X Games event.
I just bought a pair of Senn HD800's, and my Bifrost and Lyr are in the mail. Would never have even considered changing the tubes until someone in the thread I started made the suggestion. Seems crazy to even be considering it before I even listen to the gear, but if there are substantial gains in SQ to be had for a modest investment, why not?
So the question is "what tubes should I get for the gear described above?" I listen mostly to classic rock, alternative, and some pop.
Would be looking for improved soundstage, and substantial tight bass. Some describe the top end of the HD800's as hot, but I kind of like them the way they are. So no real need to tame that.
If I have to spend more than $200 for the pair, I probably won't bother.