Multiple subwoofers work wonders

Thanks. It's taken me a long time and is still a work in progress. Cannot stop tweaking.
One of the more interesting phenomena I've noted is that while I have been able to achieve an even flatter frequency response, the room modes were far worse. It's kind of a balancing act. 

@tcutter I see a lot of visual symmetry in the room which is quite pleasing to the eye. Did you make some aural compromises to achieve this? Or does it just happen to sound better AND be visually symmetrical?

Little physics, little aesthetics, lot of luck. Anal retentiveness probably helps. 

+1 distributed bass array (James Romeyn's version as well)

not to derail the topic, but I gotta ask: how do you like your Vinnie Rossi pre w/ your XA60.8s???

Just lovely. Tube sound was always offset by fear of reliability (had a bad experience when I was younger), but 300Bs in a preamp are pretty unstressed. It's a dual mono class A design as are the amps. In typical Pass fashion, they have a sound that has been described as tube-like, so they all play well together. The amps are direct coupled to the Wilson Benesch midrange and the music and the imaging is an immersion experience.  Very nice combination.
Midrange rules!  But bass is also nice.