Why do you want to do this? Preamps don't power speakers, amps do. Do you want to use the Sony as a pre-amp or do you want to use it as an amp?
I'm going to guess Sony as amp even tho you wrote otherwise, so connect the left and right unbalanced composite rca-type L/R pre-outs using appropriate length rca type male to male cables (neither unit has balanced connections anyways) from the back panel of your Yamaha to any pair of composite L/R rca type inputs on your Sony (pick one, cd/tv/aux/video) and use that input on the Sony (you may need to assign it to the composite input). You'll have to find a good place to leave the volume on the Sony and then let the Yamaha control it. Or vice versa.