So you did a lot today... and rather than beat your head against a wall...
I would suggest you move ahead with the curtains and such. Treating the room as you were discussing back in that other post isn't going to help you out a whole lot, I don't think.
Looking at your photos, perhaps pull your front speakers out a little more for another test when you have time. The baffle level with that front right closet is assuredly causing some issues... if you could pull it in to the room 1' in each direction, you might help minimize that.
If you can, and when you can, try opposite corner placements for your subs: front right and back left. You'll have to dial them in by ear, but if that gave your best response, then when you get them set, you should get better bass response over all in your room.
Remember with corner loading you will get significantly more output from those subs. You have to adjust them.
Consider the Mini DSP... if the $95 one will work for your situation, you can manually manage them with REW.