As I say, I haven't had a chance to compare PLIIx to EX or CES - the extra separation of discrete left and right signals may yield some clear benefits. Hopefully I'll be able to get a 990 into my system at some point to get some first-hand experience with it. PLII, however, cannot be compared to PLIIx in this context. As Sanjay pointed out, PLIIx is an extension of Pro Logic II - Pro Logic II cannot produce any signal for the surround back speakers. That's why the 950 has Cirrus Extra Surround - it provided the same sort of surround back capability as Dolby EX and DTS ES for two-channel sources that were expanded to 5.1 by PLII. (It also works well for Dolby 5.1 and DTS 5.1 sources, but that's beside the point. ) Pro Logic IIx takes Pro Logic II and adds the ability to use the same basic technology to give you two more channels. The only real differences between the two is how many channels are generated.