Sigh... I now realized when I got the first SVS sub I had dialed in three different rather extreme EQ settings trying to balance it manually in place with the location and the old Klipsch sub, and left them there. Only in the left side. So all that Dirac had those strong curves there, which no longer applied and probably made its starting point worse.
There are too many places to screw things up for the uninitiated. (Probably for the initiated as well, they just declare "I like it better that way".

)
Off to rerun Audyssey and ART again with clean settings.