There are lots of options for hooking things up. I happen to have a VCR and a DVDp plugged into the same input on my receiver. My TV doesn't have that many inputs, so I switch with the receiver.

Since the VCR needs red/white/yellow and the DVD needs Svideo and digital audio, I can connect both to the same input with the different types of connections. Digital audio and Svideo are always automatically chosen first, so I can play a DVD anytime. I need to turn off the DVDp to play a tape.

If you can figure out the details of your receiver, you could perhaps find a similar combination solution. It might be better to combine the 2nd DVDp with something like a VCR, though--something disimilar so you can use different connections.