One thing I'd like to know more about. Found this in Amazon reviews:

Q: These cancel out the TV speakers. What if I want to use TV speakers, must they be unplugged or is there a switch?

Answer: Strange. In my case, they do not cancel out the tv speakers. But I'm sure that is because I have my Sennheiser cable connected to the cable tv box. Try that. I have to have it that way because my Samsung tv does not have the compatible connection for the Sennheiser RS120 cable. But my Comcast cable box does and neither Best Buys, Samsung, nor Sennheiser could help me find any other answer.

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1986 300SDL, 362K
1984 300D, 138K