Whether you use the internal amp or RCA's...you'll have to feed the onstar outputs in-line so that the signal is fed to your speakers. Think of it this way...you have two sources for sound but they both share common speakers. Or, you could always wire up an in dash speaker specifically for onstar that runs separate from your stereo system. Best thing to do is let somebody else wire it up for you. The wiring harness you need will cost about $100 so that your stereo can be integrated with your vehicle's RAP system.
