7 or 5 speakers

as far as i know, you don't lose any information by going with 5 speakers vs. 7. the sound to the rears is taken from what is already going to the surround speakers if movie is dts or thx ex (dolby) 6.1. there are no 7.1 encoded movies to my knowledge and even 6.1 movies are hard to find. with 5.1 encoded soundtracks, rear speaker info is matrixed from the surrounds.
7 speakers may be worthwhile in your room if you have enough room behind the listening position to properly position the rear speakers.
most people i've spoken with including robert harley (tpv), feel that there is not much difference between 5 and 7 speakers. i've wired for the 6 and 7 speakers in my ht, but have yet purachase/install them. caught audio bug instead. i don't know anyone including dealers who have 7.1 systems, so i'm not speaking with any first hand knowledge.
as far as the sub goes, all i can say is that i run a single earthquake mkv 15 inch sub in a 19x45x9 room with no problem. subs volume at 25%. room is not enclosed. (opens to another room.)

aloha keith

In response to Redwoodgarden, the only speakers I don't have are rear and the possible side ones. Decoder is a Lexicon DC1, main speakers Mirage M3si. Rear and side amps are Adcom GFA 535. Seating position is 16 feet from front wall, so about 12-13 feet from screen.

7.

With the stock decoding algorithms on 5.1 sources, you get a bit more immersion from the side + rear surrounds. THX-EX encoded source will put sounds arround, beside, and behind you. Your Lexicon will also enhance pans from the front to rear speakers. My upgrade from 5.1 to 7.1 with a Lexicon DC-1 was worthwhile.

As far as the sub:

Home theater bass requirements for reference level LFE playback are ludicrous. Few commercial sub-woofers will not reach 115dB @ 20Hz @ 10% distortion.

My HT room is approximately 13' x 19' x 9.5'. I originally had a 5.1 set up, and used two side speakers (tripoles) and no rears. I then expanded to a 7.1 set up by adding two (monpole) rear speakers. For me, the improvement in sourround envelopment with 7.1 was significant, so much so that I will never go back to 5.1.

I listen to everything in 7.1, independent of source. I use Logic 7 in a Lexicon MC-12 to generate 7.1 outputs from any source.

Recommend you search through AVS Forums for posts by Sanjay. He has articulated several times why a 5.1 set up (whether that means sides and no rears, or rears and no sides) cannot give the same surround envelopment as a 7.1 system.

Thanks
Bruce

Homer, it sounds like you are all set for 7.1 except for the surround speakers. You can get excellent surround speakers at a moderate price by concentrating on high quality midrange and tweeters. Don't worry about the bass; it's not that important for movie surround speakers. Forget Bose speakers; they don't have any detail.

I would still recommend a second sub and put both in corners. Most HT that I have seen have a loose boomy bass that turns me off cold. Placing the subs in corners make them produce sound that you feel in your chest.