Dan, Is that a refrigerator next to your upper couch? Is it possible to replace it with your sub, temporarily? Might help with the LFE for the upper seating, but may compromise the experience in the lower seating. There aren't many HT's (that I'm aware of) with seating presenting such extreme variables, so you are in uncharting waters here. Give it a try and let us know how it turns out.
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"Never, never, never give up "... Winston Churchill