This is how you have to hook-up your system: The processor you are going to buy has six or eight outputs. The number of outputs is not important, what is important is that first you buy the number of amps that you need to drive all of your extra channels like your center, your rears, your sub, and that you use your existing amps for your front left and right. Now you say that you have a processor loop on your two channel preamp; the processor loop will let you bypass the volume control from your preamplifier. In order to achieve this you must connect the front left and right output of your processor to the processor loop of your two channel preamp(your preamp must of course still be connected to your main amp!). Then you must connect all the other outputs(center, surround, sub) straight into your other amps. This set-up will give you the best of both world. The processor will not affect the audio signal when you listen in two channel audio as it is not in the signal path. And when watching a movie you have total control of volume with your surround processor, just remember to turn on your two channel preamp and to switch on the processor loop. Hope I waasn't to confusing in my explanation. Cheers.
2-channel to 5-channel
I presently own a 2-channel set up and would like to incorporate 3 more channels into my sytem. I presently have a pre amp that has a processor switch that allows me to incorporate but I'm not sure how this works. At first I thought that I could buy a dolby digital surround processor hook it up through my surround loop but where would I hook up the rest of my speakers meaning the center and surrounds? My pre amp doesn't have the additional speaker posts for a home theater hook up. I hope I didn't confuse anyone with my questions. I just want to know how this process works and if it's better to just purchase the Vantas unit that incorporates into 2-channel systems?