Purk, I was about to congratulate you but I realize we need a little more effort to push you over the edge
. I must warn you though, there's no coming back!
More seriously, looking forward to reading the impressions from someone as experienced as yourself. I can't say for the T2 / BHSE but I can't imagine you getting deceived with the 009 out of the 717 amp coming from a HD800 rig.
I personally had to perform more drastic mod than recable to make the hd800 to my liking so I can't imagine you being turned off by the 009 tonality for instance. Besides this proclaimed brightness irritative to some and unless you like to listen rather loud, it's delightful!
By the way, as for the "brigthness" of sr009, actually it's more in the mids/upper mids rather than treble that people might have issue I think. The treble is very resolved and natural and it isn't sticking out in the least bit. The issue from some people with its "brigthness" is a problem with the overall voicing (and optimal listening level which is much lower than something like the omega 2). In that sense, the hd800 issue is a little different with a peak in the upper mids that sticks out and needs attenuation (and probably the scoop in the mids below that, see what anaxilus and co have done recently over at purrin's forum, it seems quite promising).
For soundstage, I prefer the precise layering and placement of the 009 to the extremely wide / deep albeit slightly fuzzy soundstaging of the hd800 but some may prefer either one based on tastes (also the hd800 seems to keep improving with the amplification, I did not looking something better than luxman p1u).
In the end, if you have the disposable income and the upgraditis itch, I don't see a reason why you you stop yourself (evil grin). We are way past the fotm fever at this time, and you've already tried it a bit so it's not like you may be completely surprised by what you get.