"The problem is the broadcast source, not anything in your house"

I don't think this is true, after reading his post.
To me it sounds like the TV volume control is 'preamping' the line out signal. If the TV is left up or down, next time that input is selected can be an alarming experience.
I've had TV's that do that, and others that don't
I prefer the latter..
..and again, I think it should be a standard spec to have it NOT controlled by the TV speaker volume.

That said, there are many times I think that DVR you mentioned would be a great investment, but every time I have $$ I find something else I 'gotta have'.

Mac's advice is the hardware solution Original Poster was looking for..

I do not work here, but the benefits are still awesome
Make your sound your own!