Well, if your receiver has a preamp-out/amp-in loop, you simply plug your new pre-amp into the amp-in plugs on the receiver. That way, you'll be using the new pre-amp as your pre-amp, your new tuner as your tuner, and your old receiver as your amplifier.

This is what I did when I went from my old Onkyo TX-DS939 receiver to my Lexicon MC-1. First, I replaced the pre-amp and surround processing with the MC-1. Then I replaced the amplification, and finally, I replaced the tuner and was running all seperates.

Jeff