I'm in the very fortunate position of owning a complete KEF THX TDM speaker system comprising 5 monopoles and 2 Dipoles. For 4 years, I have had the dipoles in the Surround L&R position and the monopoles in the Surround BAck channels as recommended for THX Ultra2. However, I've been thinking recently (after hearing more detailed surround effects in inexpesive systems) that there might be some phase cancellation going on in my system between the dipoles and the monopoles at rear. So, as an experiment I swapped the dipoles to the Surround back channel and put the monpoles on the Surround L&R. The result was much much better for 5.1, but back channel on EX soundtracks was practically inaudible and again appeared to disturb the balance of the rear L&R speakers. Then I removed the £700 TDM34 dipole speakers completely and replaced them with a pair of £79 monopole speakers. I bought some wall brackets and stuck them on the surround back channel. The result..... what the hell have I been doing to my system for the last 4 years? My system is now equally breathtaking on both music and fiilms. Sound effects are more detailed, and the existing THX monopoles make 5.1 music more natural and balanced. Dipoles are good for spacious sounds on old fashioned Dolby Pro-Logic but for anything else they hold back the performance of your system. So my advice to anyone thinking of buying a pair of dipoles for your system is think twice.... try them at home first. I've been blindly using them for 4 years, and I've been strangling my system.