So I have a pioneer VSX-823-K receiver which I want to connect to my houses surround sound system. The surround sound is currently coming from another receiver thru it's preout port. Can I just use a speaker wire to rca converter? It is only a temporary solution cuz that's all I need.
Also, I want to use the pioneer because I can hook it up to my other 135w speakers where as the other amp only can handle 75w output
No. Speaker level and line level signals are electrically different. If the preamp out is being used with the current receiver, then there is another amp in the system somewhere. The Pioneer is not intended to drive another amp, it does not have the correct outputs.