Pro Logic II will take a stereo source (analog audio, PCM, or Dolby 2.0) and generate 5.1. Pro Logic IIx is essentially the same as Pro Logic II unless you have surround back speakers. If you have surround backs, Pro Logic IIx will generate 7.1 from stereo sources and will do the same with 5.1 sources such as Dolby 5.1 and DTS. It is comparable to the 950's Cirrus Extra Surround, except that it generates discrete left and right surround back channels - CES (and Dolby EX, DTS ES, and DTS NEO:6) only generates a mono surround back signal.