Question:  Does the 2nd tuner (PiP) on your dvr output sound?? All the DVR's I've seen don't have sound.  If sound is not an issue, then:  If there is an open frequency that your local cable provider has no carrier wave, then I don't see a problem.  Make sure your insertion equipment output is only 6-Mhz wide and you should be fine.  I know some systems where they state that your selected frequency is based on "center frequency" only and doesn't keep a tight bandwidth.  Those insertion systems bleed over into other freqs. and cause problems.
Worst case, you can always put a notch-filter on the freqency you want to take over, then inject your feed.  There's a few ways to accomplish what you're looking to do.
Good Luck.
    
    Re: Channel Insertion on house system
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