bi amping Von Schweikert vr4 jr

I just read a review by Rick Becker where he bi amped the vr4 jr with a five channel amp. My question which I hope is not too stupid is how do you get a stereo signal out of 4 channels (2 rights and 2 lefts) of the prepro to the amp? I have a lexicon DC-1 and a Harmon Kardon PA-5800. Thanks, Wade