I've optimised the placement of my front LR speakers for stereo, and I have a center speaker and two surrounds lateral to our seating position. CD and SACD disks are played in stereo, most DVDs in 5.1. Frequencie below 80 Hz are shunted to a Velodyne HGS-15 whether in stereo or 5.1 -- I suppose stereo might be termed 2.1.
I see no reason for an either or decision in this matter; you can have both. I find that by shunting LF to the sub, the LR speakers sound a bit more open and transparent in stereo, and the sub integrates seamlessly so you would never point to it as a source, and it can deliver the subtle vibration you feel when you attend a live pipe organ recital. I like to experience the canons wizzing over my head when watching Master and Commander, so when 5.1 is available for movies or some TV shows, especially CSI: Miami which is so spectacular in HDTV, I tend to use it. But I have found audio DVDs more of a novelty than an enhancement.
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