You will need to spend at least 500-600 for a used pre/pro (Sherwood Newcastle 9080 abd Sony 9000 spring to mind), but if the rec and int do not have pre-out/main-in connections, you can't use their amps. You're probably better served with a receiver. There are a bunch of good new and used ones out there depending on your tastes and price range. Can you give some more detail? Budget, composite/S/component video, intent to move toward full HT, etc?
AV PreAmp vs. AV Receiver
I would like to be able to easily switch from VCR to DVD to DVD/CD use in an inexpensive 2 channel system by/for the TV. I have a cheap (in place) Onkyo two channel receiver and another integrated amp that can be considered for use. None are "AV" designed. Would I do best to get a cheap new "AV" receiver, or would the addition of an "AV" preamp give me the best performance, (within the same price range?) This is not for critical listening, just for TV/movie sound and background music. Will be pumped through some PSB 300i speakers. May add a sub later. Thanks for your help. Charlie