So in my 2nd. impressions I mentioned that some recordings acquired an unpleasant thump, whereas other tracks that I consider dark had no perticular change in their profile.
I am starting to suspect either a placement problem or a tuning/software mistake.
I decided to check how they sounded with fewer than 3 active cells. I started with just 1. No spatial sound. But also no thump. Hmm.
I then added the 2nd. cell, and in the process moved it a bit further away from the wall (now 2ft as recommended instead of 1ft.). Now I got spatial sound, but also the beginnings of a thump.
Finally I moved the 3rd (rear) Cell to be both more centered behind me, and further away from walls and other obstructions. No real change in the spatial sound - expected, as I still don't have access to 5.1 inputs - but also no particular change in the tonality/thumping. Still there though.
My guess at the moment is that there's either a peculiarity in my room or placement, or a resonnance in the bass spectrum that the Syng software is sensitive to, ot I guess rather NOT sensitive to. It truly sounds like there's a few deeper notes that acquire positive interference and get strongly amplified.
Still playing around with that over the weekend. I still hear that particular rumble in some cases, and it's unclear to me if it's something that's supposed to be there in the mix (it's from a movie) or a tuning/placement/software issue.