If you want hd to the second set, use the component outputs. You will also have to connect the audio if you want sound since component only carries video.
If you want to use coax, then an old vcr will work fine. Connect the red, white, and yellow from the receiver to the vcr, then use the coax out from the vcr to the tv. Make sure the tv channel is the same as the output setting from the vcr, either 3 or 4.