Room help

Forget WAF. Orientation with the speakers facing the long direction and space behind you is correct.

Diffusers are a band-aid.

Still struggling with a similar situation myself. Suffice to say it’s complicated. Our ears interpret reflected noise and try to line them up. At best, we interpret room reflections in such away that the sound stage is wide and - most importantly - deep. I believe any treatments or dealings with the brick wall would have an absorbent affect and would not give you what you need - which is the even order harmonics that trick your brain into thinking the sound is coming from behind the speakers in front of you. You could get a cheap mic, test your current set up, reconfigure, test again, and then keep moving around until your long wall configuration matches the results of your preferred sound. My gut is that you will need to pull your seat out further from the back wall, push your speakers further apart and into the corners, and still you will end up with a dead space between the speakers where the bass should be. 
 

Absorption will only get you so far here. It will remove unwanted reflections. What I think you need is more correct reflections that the width of the room doesn’t allow. To test, try moving two large surfaces into the room - bookshelves or plywood. From your seating position, look behind you and imagine a 2 bumper pool shot that would get you back to your speaker - 1st hit the back wall then hit the temporary panel. Make sure the panels are out wide enough not to be inside the 1st reflection point zone.
 

This is what your narrow setup is doing. The sound hits the side walls, then the back wall, then your ears. You interpret the sound as coming from the speakers in front of you because it hit 2 surfaces (1 surface would cancel the sound out) and since the sound took so long to hit your ears, you interpret it as coming from further away - ie deep behind the speakers. Because bass frequencies hold up better in time, the bass tends to step further back in the sound stage - and now the instruments sound more separated. 
 

I have gone so far down this road as to add rear surrounds out of phase with the front speakers to aid in the illusion. The are directed at the space between the speakers in front of me. This actually works but at the cost of imaging. 
 

I’m not an expert by any means - but I would say try to experiment and do what you can to understand what is happening before you start purchasing permanent room treatments. 

Thanks for all the responses! 

I will continue playing around with the setup.  I'm really fascinated by the process.  And moving stuff costs nothing.  

I'm also reassured that this is not just an easy solution that I am simply too inexperienced to figure out quickly.

@zazouswing +++, but - - - on the rears.

@likat - our room is an almost duplicate of yours, including being upstairs with a staircase at one end. I had 8 foot custom bookshelves made that sit outside the speakers which act as diffusers. Blinds over the window and quilt over the TV. Pulled out the W/W carpet and installed Ultra hard strand bamboo floor about 75% covered with thick wool area rugs.

The missus wanted it the other way. She hates saying "You were right"

The System

@likat , Your problem with the original orientation is that you are sitting way too close to the rear wall. You can try and add a lot of absorption to the rear wall but it will never sound as good as the new orientation. As a rule of thumb you want the listening position in the middle of the room with the speakers in a symmetrical situation. They should either both be next to corners or both along a wall away from corners. Both speakers near corners is better for bass but it puts an early reflection right next to the speaker which should be deadened. All this depends on the type of speaker you are using. I am assuming you are using a point source dynamic loudspeaker and not a panel speaker like a Magnepan. Symmetry is crucially important for stereo systems. Any variation between the two channels blurs the image. Achieving perfect symmetry is not easy. No two speakers of the same make and model are exactly the same. There will be slight variations in frequency response. Add the room and you can get wild variations in frequency response between the two channels. All this can be managed depending on how much money you want to throw at the problem. Getting any system close to perfection requires a measurement system and microphone ($300 at Parts Express) and digital signal processing (another $3000). Trying to do it by "ear" the old fashioned way is like duck hunting with a sling shot.