There appears to be no way of stopping the TiVo from sending a signal through it's RF output, so if I want to play a videotape, I have to physically unplug the output cable from the back of the TiVo, otherwise it clashes with the VCR output.

Why use a combiner? The way I have it set up, TiVo sends RCAs to VCR(Line Input 1), VCR is always on, sending RF to TV chan. 3. When I play a tape, the VCR ignores A/V in anyways.
It's great because I don't have to change the Stereo's input either (Always VCR). Even DVD's go through Line Input 2 on the VCR.
Is there some reason you need the combiner (Only 1 Line input to VCR for TiVo & DVD?)
Jason

_~= Dearing =~_
"WAY too happy about having #99."