So there is the room. its 18 x 15 foot roughly. I have a kitchen that opens on the right. Couch is about rule of thirds from back wall give or take. The kitchen side down that wall then leads to rest of ranch style house. Hall way and such.
The sensitivity of the center was specified at 91 dB, 2 dB higher than the left and right. Depending on the impedance difference, it is possible for the center to be effectively a few dB more sensitive than the left/right, i.e. the S38. So if the L,R were set to -3 to -4, the center should be around -5 to -9 but not -12, unless the center speaker is much closer to the main mic position.
You should perhaps run Audyssey again,, and this time be sure to follow the instructions to the letter. I would also suggest you lower the subwoofer volume to 10 O'clock. I know owner's manuals quite often would suggest 12 O'clock, but based on the result you are getting, 10-11 O' clock would seem more reasonable.