I am constructing a 12x15 HT with two rows of sofa seating. The back row seating position will be approx 3 feet away from a book shelved back wall and the front seating position will be approx 3 feet in front of that leaving 9 feet to the front wall. I should note that the back row of seating will be 18" higher that the front row.

My question is for a 6.1 surround system, does it make sense to have two sets of surrounds to the sides of both sofas wired in parallel or place one set of surrounds in between the two rows?

Also, with the back row being 18" higher than the front row, should I angle the back surrounds so that the front row will hear them also?

My question is for a 6.1 surround system, does it make sense to have two sets of surrounds to the sides of both sofas wired in parallel or place one set of surrounds in between the two rows?

Not needed. Side surrounds can be even with or behind the first row and even with or ahead of the second row. One can sit behind the side surrounds in a 6.1 or 7.1 layout and still have a good aural experience. There is latitude in the Dolby suggestions. Room for a second row.

http://www.dolby.com/images/consumer/home_entertainment/room_d4.gif

Also, with the back row being 18" higher than the front row, should I angle the back surrounds so that the front row will hear them also?

Again not needed. Sounds are only so so directional (the famous example is that you can still hear a speaker when standing behind it). There may be a slight HF roll off for those not directly on the axis of the tweeter; but the surround field is intended to be defuse.

I have two rows of seating, and originally had 1 set of surrounds set up for the back row. The front row didn't get enough surround effects for me. So, I bought a set of matching speakers and wired them in a series with the other surrounds. Much better sound in both rows with this setup. A real theater has an array of surround speakers, no reason why a home theater can't.

So, it works either way. I like the way my theater sounds with 2 sets of surrounds.

By the way, you probably need to wire the speakers in a series, not in parallel. (YMMV depending on amp & speakers.)