Audiopoints beneath Thiels are a great idea -- I found that they make a very noticeable difference. Glad you did that, but you already took my first recommendation. My second is to go to MIT and you already did that too. ;-)
So, let's go far deeper into the bag of tricks. First, how long have you had the 3.6's? If you are real handy, you may want to consider replacing the caps in the cross-overs. High quality caps all have their own sound -- you might want to contact Thiel and inquire about the need for replacements after x years, the type of recommended replacements and whether that should be done by a pro.
Second, I assume you've tweaked the speaker placements. If not, that's always a great thing to do -- and very time consuming. There are lots of good threads on that here.
Third, have you tried the Porter Ports? i.e., the cyrogenic outlets from Albert
Fourth, did you decide to stick with the stock tubes because you prefer them to others? If not, some tube rolling might be fun. Sorry I have no suggestions here but there may be threads on that topic (or you could start a separate one if no suggestions are forthcoming).
Fifth, what about acoustic treatments? Are you using any now?
Good luck.