Well it's taken me the best part of a year but I have finally got a full matching 6.1 system. Polk Audio: Fronts L/R RT600i's Centre CS400i Surrounds F/X500i's Surround Back RT25i Just thought I would post my findings as it may help others when thinking about purchasing speakers/packages, also a mention on Direct radiating/Di/Bi-poles for surrounds and positioning of the surrounds/surround backs. I started with the Polk floorstanders and Polk centre giving preference to the front soundstage, I was on a budget like so many of us and couldn't afford the full system, I already had a pair of Tannoy MX2's for the surrounds so decided the quickest and cheapest way was to buy another pair for the surround backs, at least the back soundstage was the same even though it didn't match the front. I then found the centre (CS245) was being out classed by the main fronts so I upgraded to the much larger centre, in fact I was more worried that the centre would outclass the mains, the CS400i is a monster, weighing in at 30lbs, but it's size and weight only helped it to make all the difference, when I played the test tones across the front the sound from each speaker was now identical so I knew this was to be a better match. The proof would be when listening to a movie, especially dialogue, there's nothing worse than having dialogue lacking in depth from the centre then it sounding like James Earl Jones from the mains. So after a few demos I sat back in the knowledge that I had chosen the right speaker this time as there was no tonal change when listening to dialogue/cars/trucks/planes etc when it's being steered through any of the front speakers. This just left the rears, I started with the surrounds so at least when I was listening to 5.1 the system would match, I wanted to choose the right speakers for this (having learnt my lesson earlier with the centre speaker), so I looked mainly at the drivers and selected the ones that were the perfect match to the fronts, this was so that any soundtrack with steering from front to back, back to front etc there wouldn't be noticeable change in the sound tonally. The results were perfect. The system was coming together nicely. Only the surround backs to go and this was where I started to get confused, do I swap the surrounds and place them at the back for the surround back duties and buy a pair of Di/Bi-poles for the surrounds, or just buy another pair of RT25i's and be done with it. There has been a lot of discussion just recently on the subject of Di/Bi/Tri-poles, some love them, some loathe them, so I decided to give them a demo, I was pleasantly surprised, not the mish mashie sound I always thought they would produce but the F/X500i's gave a very clean sound just what I was looking for. The clip from Twister did it for me, listening on my system with the RT25i's the sound of the wind whistling round the room tended to be coming from two open windows to the left and right of me and not all around, but with the F/X500i's you were sat right in the middle of the tornado. These speakers have the option to produce a more direct sound if needed, maybe for music, all you have to do is switch them to Bi-pole, I listen to music via Direct/Stereo so for me I can't see me switching it to any other setting apart from Di-pole for the time being anyway. Now to my last decision, shall I use a single speaker like I am doing at the moment or a pair of speakers like I have done in the past for the surround backs? I still have the same view on this, if the pair are being feed the same mono signal and have to be positioned just about on top of each other why bother with a pair so I have stuck with the single surround back for now, at least I won't have to spend more money upgrading as I have the other extra speaker when 7.1 does finally arrive. Saturday night was the first time we were able to sit down and watched a movie on the completed system, Sum of all Fears was the choice; all I can say is WOW! Such a difference, everything just blends in, you can really tell the difference from a full matching speaker system to one that has been put together from different manufacturers. As for the positioning, the surrounds which are in Di-pole mode are on the side walls approx 90cm above ear level when seated and level with the listening position, the surround back is directly behind the seating position approx 2m, it is slightly higher than the surrounds and I have also angled it downwards very slightly. Yes it has taken the best part of a year to get to this stage but it has been worth it.