Replying to myself:
As of now, Dirac did not reply to my ticket re stereo vs. multichannel filters. Therefore, I called Emotiva (my processor is an XMC-2) who said that I should definitely create two speaker settings, one for multichannel and one for stereo, and run Dirac separately for each creating two sets of filters.
I did this with my currently connected set up, which is 7.1 as follows: XMC-2 - Buckeye Hypex 8-channel - seven Revel F206 speakers and a Rythmik F12 sub. The multichannel reproduction has been great, but I was not entirely happy with stereo sound quality, consequently I ordered a pair of Revel F208s, which I never set up and returned for reasons below.
I won't bore you with any detail of my subjective impressions other than to say that the separate stereo setting and Dirac filters (with NO sub, just two of the F206s) was a significant improvement for stereo reproduction over the 7-channel filters. Incidentally, Dirac equalized the speakers generally flat down to 32 Hz, easily meeting my needs. For the ten minutes it took to create a separate speaker setting and run Dirac, I believe that this would be worth trying for anyone with the capacity to creates the extra setting and a slot for the filters.
Thus I returned the F208s on a cost-benefit analysis (money and effort, they are big) and because I wanted to retain the seamless multichannel audio quality resulting from uniform speakers. Hopefully this will be useful to someone else out there is ASR-land.