I've just installed an amp and a hands free phone system on the front
speakers of my car.

The handsfree phone system sits between the iso plug on the head unit
and the iso plug on the wiring loom. It can interrupt the head unit
output on the front speakers with that of the phone.

The iso speaker connections run straight to an amp and into its high
level input. The cable length is about 12ft. The return run to the
crossovers is about 15ft.

I can detect a slight hiss from the front speakers when there are gaps
in the audio.

Would connecting Line out adapters to the speaker output next to the
iso plug then running an RCA cable to the amp be a better setup or
would it make little difference?

TIA

James.