You need four-conductor cables for the two front speakers, as max says, instead of the usual two conductors. Most speaker cable companies make them, or you can just use two runs of standard cable for each of the front two speakers. Then you remove the metal links connecting the terminals on the rear of the speakers, hook up the cables at the speaker end, and the Sony manual explains how to configure the receiver to biamp and connect the cables at that end.
But as max also says, this is something a good retailer should be able to explain and demonstrate for you.