My bedroom HDTV has a QAM tuner built in. So I get all the unencrypted digital channels, including those in HD, from my cable service.
However, I do have an HD set top cable box in the family room that handles the encrypted digital channels, and it does have an auxiliary video output which always outputs SD even when it is tuned to a HD channel. Basically, it letter boxes the HD. I use that output with my video sender. Yea, it is only SD, but it is usable.