5.1 to 7.1

So question is this. I run a 5.1 system with all Axiom speakers, 99% for Home Theater. My current receiver is a 7.1 Receiver, so I an wondering if its worth changing to 7.1. Furthermore I run QS8's on the sides of my stage, so do I honestly need to run QS8's in back too? Or would a simple pair of QS4's and even M2's be just fine for the back speakers? I have a Cambridge Audio 640R if that matters. Thanks
A better question might be how many who have 7.1 are going back to 5.1?

Depending on how well your receiver does 5.1-7.1 matrixing, IMO 7.1 is far more entertaining by creating a larger surround with more discrete rear channels.
Room size is not an issue.

You'll get the best success by using matched speakers, no dipoles.
Actually, I think room size is an issue. If you are going to put the 7.1 speakers within a foot or two of your listening space then they can actually detract from the sound. If you have multiple feet behind the listening area, they can add. But too close and they just become point sources. Some people put the back speakers on the floor behind the couch/chairs and pointing upward. I tried that once and found it quite unsatisfactory. If you have enough room, they can really fill in the sound. But, IMO, you need space behind to make them really worth will.

FYI - I have a 7.1 theater with plenty of space and the back speakers really add. I have 7.1 in the family room with only a few feet behind the chairs and the back speakers are interesting but honestly do not add that much. They are too localized.
If you have some extra speakers of any kind, just run some wire across the floor and give them a try. It will at least give you an idea of the look and the sound.
I have my QS8's on stands now for a 5.1 system. How far away should the surrounds be from the listening position. it makes it hard when 2 people are sitting on the couch as each is closer to one speaker then the other. I did measure the put in the delay from each speaker from the middle of the couch. Of course when we watch movies, its me and my wife, so neither is center,
Think of the same triangle rule you use for your fronts. I would suggest 5 feet back, which is hard for most people. You can also consider 6.1 which takes the stereo issue out of the picture. You can also use 6.1 with 2 speakers in parallel.
>So I an wondering if its worth changing to 7.1.

Yes. It's a quantum improvement in envelopment.

>Furthermore I run QS8's on the sides of my stage, so do I honestly need to run QS8's in back too?

Sound tracks mostly place ambiance and effects in the surround channels so you don't need to worry much about musical accuracy.
Thanks.... Since the wife has now heard the 5.1 system and loves it, she has set me free! So while my receiver is in for repair, I ordered new wire for everything, upgrading from Radioshack clear 14awg wire, to Canare 4S11. I bought Silflex premium glass toslinks. (Very Nice) I am going today to get 250' of Romex 10/2 and am going to run two dedicated lines, one for the amps, and one for my digital. Lastly I am stuck on the outlets. I assume you would want the best you can afford on the amps side, but would a Porterhouse be fine for all the others? I was thinking of running the Maestro on the Cambridge Audio receiver and Rotel amp to my VMPS sub.
Well to update..... I have run two 10/2 Romex wires, one to my Receiver and amp for my sub. And the other for all the digital. I went with two Maestro plugs, for the amps, and the CD player, and DVD player. I went with e MIT Z Duplex for the Plasma TV and HD Cable box. I put one extra Porterhouse in each box, for anything else I may need.

I also upgraded my speakers from Axiom M22 front to Swan Diva 5.2F's and all I can say is WOW! I still love my Axioms for HT, but for music, hands down the swans are much better.

I also got Swan 5.2R's in the deal, but I dont see any stands for Swans Dipole speakers, so they are sitting in a box for now.

I have yet to test out the receptacle's as they are not hooked to the box, which I plan to do tomorrow.

I will further update for sure!
OK last update... I think the MIT Duplex is the biggest winner. My wife first said Oh my.... baby it looks like I have a new TV! Much later we hosted a Football party, and I heard many people say the TV upstairs has a much better picture.... Well the TV upstairs is a 7 year old Pioneer Plasma but hooked to a MIT Duplex Z, while the TV downstairs is a 1 year old LED LCD Samsung, but hooked to a standard plug. Needless to say, I now want to get More MIT outlets for all my other TV's.

As for all the other wire and plug adjustments all I can say is WOW myself. Again the Football party lasted till about 3am while a small group just stood in front of my system and jammed to a few CD's saying... "dude the is like being at a live concert! One asked how, with the system so loud, was there no noise between songs....... I just smiled..:-)

Of course all this makes me hungry for even better equipment. And as I said before... I wife can hear the differences in my system which will help justify future equipment.