Looks much better but as you mentioned you must move the couch between the two rears.
Hopefully your recevier will allow enough fine tuning (e.g. setting the value for the distance of the rears individually)
If the sub will work back there is difficult to tell. Usually a sub will be in the area of the fronts (between left/right and center to start with) but usually this depends on the room (as usual

).
This is something you have to test in any case. Most likely you have to change phase to 180°, if the bass sounds a bit weak compared to the default setting.
One note: Maybe the fact your room is not the standard rectangle can give you an advantage in terms of reflections.
I wish you good luck and maybe send us a note how it went