Welcome, 249. My first thought is that I'd like to set up on the north wall, despite the window. What you propose now doesn't really seem suitable for 7.1, since the two back surrounds are supposed to, well, surround from the back. You don't appear to have either enough room behind the sitting position, or a full wall to give a good effect. Staying at 5.1 with that seating arrangement might be a better idea.

-----------------------------------

Enjoy the music, not the equipment.