I'm in the midst of finishing a dedicated room in my basement. The room will be about 15x22 with two rows of seating. I have RF-7s and RC-7 for the front, RS-7s for the sides, and RB-75s for the rears. My plan was to build boxes to allow me to sink the RB-75s into the rear wall making the front of them flush with the wall, but due to obstructions behind my room, I could only do this if I had 4 feet between the rears(each one 2 feet off the center of the room). That seems WAY too close!
So, I am thinking about purchasing another pair of RS-7s for the rears, and using the 75s somewhere else in the house. Hung on the wall, I could spread the RS-7s so I have more like 6 or 7 feet between them. My question is how much sound quality am I losing in my HT by using the RS-7s rather than the 75s? The bookshelves seemed perfect for surround back speakers. (Note: I'd guess the room will be used 80:20 movies:music.)