I have recently upgraded my home theatre to a 7.1 set-up (7 speakers), adding a pair of Mission m7ds and mounting them onto my back living-room wall and pairing them next to each other. I spent most of today playing most of my dvd collection containing a mixture of Dolby Digital/DTS 5.1 soundtracks and I have come across a fundamental difference between playing them through 6.1 "MTRX ON" & "NON MTRX" and heres the breakdown between the two: 5.1 soundtrack via 6.1 "MTRX ON": Sound signal coming from the 2 surround-back channels is in 'mono' - meaning the SAME SIGNAL is coming out from BOTH surround-back speakers. 5.1 soundtrack via 6.1 "NON MTRX": Sound signal coming from the 2 surround-back channels is in 'stereo' - meaning there are 2 DIFFERENT SIGNALS coming out from the surround-back speakers and this IMHO creates a smoother transition between sound panning from the surround-left to the surround-back, and to the surround-right speakers. Regardless of what 6.1 mode you use, they both do a good job of creating a convincing sound-field from behind the listenning possition. IMO though, I prefer to use the 6.1 "NON MTRX" mode, as the stereo surround-back signals (although matrixed) offers a more fluid transition between the surround speakers (SL, SBL, SBR, SR). Has anyone else made this observation? PS. For movies that contain Dolby Digital 5.1 EX, I take it I switch the surround setting to 6.1 "MTRX ON" to achieve the best results?