1.If the surround are mounted alongside and slightly to the rear of the seating area on the side walls,at 2-3 ft. above the listeners (or at height level when standing) at what distance from the ceiling and rear wall should i mount them to not enhance too much the bass?
I wouldn't worry too much about this as generally surrounds won't be putting out too much bass. I would just recommend putting them 2-3ft above ear level when sitting at the angles specified in
this article.
2.Is it necessary to buy a wall mount for surrounds to aim to the listeners aria or as dolby says i will stick to their way which is mounting on opposite side walls facing towards each other?
In the end even speaker placement can be a subjective area with some people preferring different things than others. I would recommend placing them how you like them, so experiment. I know many people prefer to have their surrounds slightly behind them and towed in some no matter what Dolby recommends. Also, you don't have to wall mount your surrounds, you could also look into getting speaker stands for them.
3.Is it absolutely necessary to align the two standfloors and the center on the same imaginary line?I understood from the zilion tutorials i've read that the 2 standfloors should be at the same level with the top of the LCD line,giving that,the center is above the LCD only the bottom of the center will be in the same line with the standfloors and lcd.
(personally i would like this because it saves me some space under the lcd)
You will want the two floor standing speakers equidistant from the center of the display if possible. Also, you will want to try and position the speakers so their tweeters are at about ear level. The center and floor standing speakers need not be the same height.
4.Is the position i figured for the subwoofer in the back left corner of the room o.k.?Or should i consider another option?
Placing a sub in the corner will result in more output do to room gain, but can also make for a more boomy sound. I suggest you place your sub according to
this articles suggestions.
5.As you allready probably noticed the impedance range of the speakers is in between 4-8 Ohms (?!?) My receiver has an andjustable impedance range (6-16).Should i choose the 6 ohms receiver impedance ?It makes sense for me,beeing a number between 4-8?At the end this impedance is not a straght line?It moves uo and down like a parabola?
Impedance changes depending on the frequency being played and is not a parabolic or linear graph. I would leave the receiver on its 8 ohm setting and not worry about it. If there are problems you will hear audible distortion when the receiver strains and the receiver will go into a "safe mode" if it can't deal with the speakers. As I said though, this won't likely be a problem.
6.If i keep the receiver impedance at 6 Ohms would that hurt my sistem when the impedance goes down to 4 ohms ?
Very unlikely, but I would still put the receiver in the 8 ohm position.