You have to enable the volume punch through on each device you want to use it with. I got thrown off by this as well when I first got the 950. To use volume punch through with the cable box and TV, do the following (from p.39 of the manual):

1. Press CBL and MUTE together.
2. Press VOLUME UP.
3. Press AUD.
4. Press TV and MUTE together.
5. Press VOLUME UP.
6. Press AUD.
7. Press DVD and MUTE together.... you get the picture

As for the plasma interference issue, I have no idea.

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