Your instincts are right. Try the short wall with the curtains behind your speakers. As an experiment, set it up without the TV between the speakers. Pull the speakers out from the wall about 3 feet and set them 8 feet apart on centers. Toe them in about 10 degrees. This will help to focus the soundstage and widen the sweet spot. Place your listening chair so your ears are about 10 feet away from the plane connecting the speakers. Make sure the symmetry is exact. Measure it carefully. Put the bookcases behind the listening chair. They will act as a partial room divider and also function as good diffusors. You could put some absorptive panels at the new first reflection points on the walls, but I would try it first without them.
This setup should give a large soundstage. Firing down the long dimension of the room is almost always preferable to firing down the short dimension. One advantage is it allows you to sit a little farther away from the speakers, which gives the sound from each driver time to integrate. The curtains behind the speakers are ideal for reducing reflections. This should be close to a LEDE (Live End, Dead End) approach which works very well. The open area behind the listening position will also help reduce reflections. Don't worry about losing the sound. The ideal case is for you to only hear the direct sound and the early reflections. Later reflections just serve to muddy up the sound.
If you must have the TV and equipment rack between the speakers, set them back at least 1 foot behind the front of the speakers.
This setup should give a large soundstage. Firing down the long dimension of the room is almost always preferable to firing down the short dimension. One advantage is it allows you to sit a little farther away from the speakers, which gives the sound from each driver time to integrate. The curtains behind the speakers are ideal for reducing reflections. This should be close to a LEDE (Live End, Dead End) approach which works very well. The open area behind the listening position will also help reduce reflections. Don't worry about losing the sound. The ideal case is for you to only hear the direct sound and the early reflections. Later reflections just serve to muddy up the sound.
If you must have the TV and equipment rack between the speakers, set them back at least 1 foot behind the front of the speakers.