My seating is also at the back of the room which is why I asked about having the speakers on the side walls. I can move the seating about half a foot- a foot forward.
I had a yamaha NP210 set of speakers and placed the rear speakers just under the ceiling pointing downwards towards the listener but I think that might be a bit too high for rear speakers.
I will take your advice and not bother buying £10 a metre cable and instead opt to buy an extra speaker. I am pretty clued up about the hardware and what things do put I have no idea about the best position.
I know I should experiment and move the speakers about but I dont want to drill loads of holes for the speakers all over the place, especially as I have just had it decorated

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I wont bother with 7.1 just yet but 6.1 does intrest me I just thought you needed a big room for 6.1.
I have a square room my seating will be at the back of the room in line with the centre speaker. I will place the centre speaker on the front wall as close to the tv as I can get it and the other front speakers equal distance apart.
It is the rear speakers I am not sure on and as I am a novice I thought I would ask your suggestiouns as you are the experts. I dont I will get the best out of them if I place them 4 foot up from the back wall in line with the front left and right speakers because I will be sititng only half a foot - a foot away from them.
The other thing I am unsure of is where to place the subwoofer? I was thinking of putting it agaisnt the side wall half way down the room.

Im sorry for so many questiouns I just have no idea on how to get the best out of them.