Hi I'm new to this forum.

I have purchased an Appradio 4 recently and have a question. I have connected the speaker wires through the power cable and was wondering, as the system has 4 preamp preouts, would they only take advantage of the built in amplifier if they were connected through the separate RCA cables, or would the amp be used even if they are connected through the power cable,

Thank you

No, unless I'm not understanding your question. The RCA preamp outputs put out a signal that is before the amp, or "pre-amp". If you use these outputs, you will not be taking advantage of the built-in amplifier. 

As rockthebeef says RCA outs are for plugging into a seperate amplifier only

The amplified outs come straight out through the iSO block connector which plugs into your existing radio harness

Thanks guys, makes a lot more sense now