7.1 speaker placement

1000 pardons if this has been covered, I could not find it in a search.

My room setup will not permit me to have the primary sitting area anywhere but against the back wall. This means that to add 6th and 7th channel speakers, they would have to either be mounted on the back wall above facing forward, on the back wall angled down, or in the ceiling pointing down.

I currently have B&W DS7's for surrounds and ideally would use the same for rears- so I have the option of configuring them as mono or di-pole.

Anyone with this room issue gone with 7.1 and how effective was it given that the rears are not behind you?

There is so little value to rear surrounds that I wouldn't, and in fact, don't bother. My rear speakers are 9' behind the main listening area and driven by very good amplifiers that I rarely power up. I also removed the center channel, so I usually run a pair of mains, a pair of surrounds, and a pair of subs. That's with the Oppo BDP-105 that I use for music and HT. The Sony XA5400ES and vinyl are stereo without subs.

I agree with tls49 and Dbphd. 7.1 should be used in large rooms, since this is the main reason it was developed. In Floyd Toole's book 'Sound Reproduction' it is mentionned that 'a large number of channels are not necessary to provide excellent facsimiles of enveloping sound fields'. The size of your room does not require the 7.1 setup IMHO. Over and above this, there is so little surround information available (if any), that it is not worth putting a lot of money on surround setup.

Better off putting your money on the quality of your front channel gear, since these are on 100% of the time. Surround effects are on 10-20% of film viewing time at best. I have a similar sized room and using only 4 speakers (no sub, film no center channel) and this system rocks and is very coherent. Your Anthem processor should provide the flexibility to use a 4.0 (my system) or 5.1 setup.
Thanks for the thought out responses. I think staying with my 5.1 setup makes the most sense all things considered. It seems unlikely that I will see any tangible benefit versus the $ expended on two more speakers and amp channels.
There's no substitute for evenly spaced speakers at ear level and a minimum of room correction. Even with my smallish home theater space, I would never go back to 5.1.

In my experience the key to decent 7.1 is matching speakers (no dipole surrounds) and not depending completely on automatic room correction. I'm not a professional installer but I've have set up a few systems for family and friends with very satisfactory results.

The most difficult was a listening position against the wall. LCR on the same plane and as close as possible to the display, The sides on stands directly to the side of the listening position and the rears mounted high in the ceilings corners aimed down at the listening position.

After the subs EQ program I ran the correction using the distance, volume, and the bass management. Manually adjusted out the EQ down to 200 Hz to taste.

Next comes fine tuning using my favorite surround queues from Master Commander (a 7.1 must).