Seems like you're kinda stuck unless you want to downsize one of the couches.
I agree that the optimal would be to pull the back couch forward a couple feet, but I see why you can't/won't do that. However, if you downsized the side couch and added a chair over in front of the sliding door, you wouldn't lose seating, but could move that back couch forward a little.
I totally empathize with you because my HT room is a similar mess. Smaller (13x16 or so) with no fewer than 3 doors on 3 different walls. (I say "no fewer" because there's actually a 4th door leading to a 1/2 bath that intrudes on 1 corner of the room, notching out a 3x4 square. >:-( Eventually, that will become a bar, but still intrudes on the space.) Plus we have duct work and structural support running along one entire side of the ceiling - reducing ceiling height from 8' to just over 7' and intruding about 20" into the room. Moving from 2.0 to 5.1 is going to be a huge pain for speaker placement.
Any other suggestions from the masters here is much appreciated!