Bass Suckout in a Square Room - Remedies and Solut

Wrayman, You are absolutely right. A diagonal set up is a good idea and can produce excellent bass and over all sound include good depth.
The sofa itself is not the problem. The problem is where the sofa is located in relation to the speakers.

Meth, you suffer from standing wave, meaning you have low pressure and high pressure points at a frequency determined by your room size. Moving around till you find a sweet spot is really putting a band aid on cancer. If you listen carefully you’ll probably hear you have single frequency bass – no matter what your playing, the full bass sound will always be around the same frequency.

You need to add low freq some sound absorption to your room. A (fairly) cheap route is to buy a few sacks of R19 from home depot and stick them into a corner. You bass will tighten up and become more natural.

Regards
Paul

Experiment with speaker placement. The distance to the front wall and the side wall should not be equal. Experiment moving the sofa forward or back. GIK makes affordable acoustic panels and traps which are also decent looking. ASC tube traps are expensive but effective.

I wonder if they found a solution?

R-19 insulation is frequency selective. If you are going to treat your room use room treatment products. I have used Tube Trap products for about 20 years. I know they work.