mouettus said:
...
BTW, how better 7.1 would be over 5.1??
How much better depends on the room and the placement of all of the speakers. Also, most films are just 5.1 (or less), though typically 7.1 processors can synthetically generate the extra channels.
If you have the space for it, and the money for it, I would go with 7.1. But if you lack either one, I wouldn't worry too much about it. I have 6.1 sound, which, in my opinion, is only a little better than 5.1. It is more important that you have good speakers, good placement, decent acoustics in your room, and that you set the balance and delays properly. If you don't get those things right (or nearly right), it will suck either way.
You may wish to go to listen to a 7.1 setup, and compare it with using only 5.1 of the speakers. Just keep in mind that you need to be careful of salespeople, who may wish to try to artificially make 7.1 sound relatively even better than it naturally does, so they can sell you more stuff.
Again, if you have the space and money, get 7.1, but do not buy lessor speakers in order to have 7.1 instead of only 5.1.