I don't know, but if he wants to get to the bottom of it he can do it, using REW. It would probably take hours though, to plot a bunch of graphs, say at least a dozen, likely more. I have no right to ask him to spend so much time on it especially he indicated he like how it sounds as it is already. If I have such puzzling graphs, I would not stop until I get it solved, even if it will take me days running REW to troubleshoot and then try various things with the Editor app.
Looking from 20,000 ft level, given the information we have now, it does point to some sort of cancellation (not phase reversal) among the 4 subs and the very deep bass capable Revel F226Be. With XO 80 Hz, they could still interact with the subs. Audyssey should be able to integrate them reasonably well, the fact that it ended up with that trough/dip, indicates to me it has to do with his setup. RC, whether is it Audyssey, Dirac, Anthem, even Trinnov, there is only so much they can do.
From ASR:
You can see that they have excellent extension down to 35 Hz, could be much more so in-room.
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