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.
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.