dolby digital EX is 6.1, it extracts an intentionally matrixed back channel from 5.1 material, PLIIx is a decoder that will allow you to get 7 channels from ANY stereo or 5.1 source, even if not intentionally matrix encoded. this includes music, movies, tv etc. also EX only works with dolby digital material with 5.1 channels. if you are using a 7 speaker setup, best go with PLIIx rather then EX for your 5.1 content so that you can have 7 seperate channels rather then you backs being mono.