Your room should be fine size for extra channels...go for it if you have the cash IMO. My system sounds great with 7 speaker setup and I may go back to that setup soon.
It all depends i guess.
I recently picked up a Denon AVR-3805, which has 7.1, and i only use 5.1
Then again, it is probably because when i renovated the livingroom i only included runs for 2 surround speakers. I coulda gone 7, but the surround backs woulda been right in the back of my dome. It is not a small room, but the rear wall is right behind the couch. makes 7.1 kinda distracting.
The good thing is that the AVR 3805 sports 3 zones, it can do 5.1 DTS in one room, power another set of all weather speakers from whatever source out in the backyard, and i can run a cheap pre-amp/amp setup for the garage.
Personally i really like the way 6.1 and 7.1 sounds, there are good enough 7 channel logic programs that will go a good job of turning any 5.1 source into a 6.1 or 7.1
In my case, i just dont have room for all those damn speakers in my livingroom
Unfortunatly the room is not the best shape for that, I could pull the couch out, but it would really shove everything else in the middle of the livingroom.
I only have about 14ft from the front of the room to the back wall, TV and all that close the distance to about 12 feet, and the couch even agianst the wall leaves about 9 feet to the TV from the foot of the couch.
Later on, down the road im planning to build a rack into the wall and maybe then i could move the couch up a couple feet.
Before i bought this house i was renting one, and i had a 7.1 setup in the basement, and there was about 12 feet to the front wall from the couch and about 12 feet to the rear wall from the couch.
7.1 sounded bitchin in that room. :)
but i still like the new house better. :)
My pre/pro is 7.1 and my amp is 5-channel. My set up is 5.1 b/c all my speakers are full size. There is no room for 7.1.
If you have room for 7.1, do it. If not, why buy 7.1 now when 9.1 is starting to flood the market. The current issue of Sound & Vision depicts a picture of 11.2 setup. 2 mains, 2 centers, 2 sides, 2 surrounds, 2 center rears, and 2 subs. Wow! Just can't keep up.
The back two speakers in my 7.1 setup are on 14" stands with the speakers facing up toward the ceiling. I only need to move the reclining loveseat out into the room about 8-10" to accomodate the stand's base. Of course, not having the couch directly up against the back wall also helps with overall bass response. My room dimensions are approx. the same as Slappys'. My side surround speakers are a bit forward of the couch which spreads the sound between the side and back out so that localization of those speakers is reduced in the back corners. Considering the room size, it works fine.
It's not likely you'll notice much difference in a room that size. I only have 4.1 (no center), with the surrounds in the rear corners on 30" stands, and surround effects are quite impressive. Seats are 3' from the rear wall and the room is about 14'x18.5'. If I had a larger room, I can see adding the surround back channels but in this room one pair of surrounds works fine.
BTW, for great surround effects, try Master and Commander. When scenes are shot below deck you can hear people walking on the deck above you. Also boat creaking noises from all directions. It's pretty cool.
Nighthawk is correct. The Master & Commander is considered a reference DVD by Sound&Vision magazine. With the proper surround setting, viewers can hear crew walking above them. In that movie, the director wanted to add less music and more sound so the viewers could feel as if they were on the ship. The canon sounds were from real recording, not digital affect. Sorry for the little sidetrack.
I have a relatively small room, about 14' x 19' x 9.5'. When I expanded from a 5.1 to a 7.1 system, there was a significant improvement in surround envelopment. Personally, I would never go back to a 5.1 system.
I've also read that a 6.1 speaker array is not a good choice because a single rear speaker causes cancellations. Even if you are only outputting a 6.1 signal, you should use two rear speakers rather than one.
AFAIK there are no 7.1 sources, so one factor to consider is how well the PrePro can generate 7.1 outputs from various sources. Personally, I listen to everything in 7.1, independent of source.
I suggest you go to AVS Forum and search for posts by Sanjay under Processors. He has some very articulate technical explanations of the limitations of 5.1 and 6.1 versus 7.1. There are also a lot discussions on surround processing versus multi-channel preamp/standard DD/DTS decoding.