I would use PLIIx rather than Dolby Digital EX. It is a more sophisticated algorithm than EX. Also, it can be used with PCM stereo and Dolby 2.0 sources. The Model 990 has surround mode memory that allows it to recall what mode you want to use for each input format type on each separate input. So the first time you play a Dolby 5.1 source with your cable box, manually select DD+PLIIx-Movie and it will remember that. When you first play a Dolby 2.0 source, select PLIIx-Movie. When you first play a PCM stereo source (which you may also encounter with the cable box), select PLIIx-Movie. The same holds true for DVD's, although if you also play CD's you may want to use something else for PCM stereo (either stereo or upsample if you want to stay in stereo mode, or any one of several multichannel modes like PLIIx-Music or 7 Stereo).