This is a tough question. Obviously a big foam couch is going to absorb mid to high frequency and will affect a room.
Usually, the rear wall and corners is the right place for bass traps.
My research on bass traps is the only effective way to make a bass panel is with membranes or very large tube traps (20 inches or so). The membrane style should only work up to 300 Hz or so and would not make a room brighter. However, the panels may be more reflective than drywall. If you are just using rigid fiberglass panels, by themselves, they would only begin to absorb above 300 Hz and can "deaden" a room. I can email you a couple of "cheap and dirty" DIY membrane trap schematics. After the holidays, I'm gonna try to build something myself.