Ended up getting the 15" sealed down firing PSA subwoofers. They are indeed dead silent, and that was just running from cheap RCA cables (not the thin ones, but cheap, thicker ones.)
Tried front corner placement, then made it asymmetrical moving one in, then tried moving both in, and it seems like having them both a quarter length in from the side walls, then shifting one a couple of feet was the best to get the nulls to not line up and to measure relatively flat with REW.
Ended up returning them because they didn't sound like the bass that comes from the Genelec 8260 monitors they are paired with.
Now I'm slowly losing hope of finding used Genelec 7271 subwoofers, and might move to Rythmik after I find something that does Dirac Live Bass Management and clearly states that and doesn't cost $4000.