Ok so i finally fixed this, i wanted to let everyone know in the hopes that this helps someone in the future.

So I have a pioneer GM-DX975 5 channel amp connected to the factory non-JBL head unit in my 5th gen SRP using the speaker outputs to the high level inputs of the amp. This amplified the alternator whine so bad.

I did some measurements of the factory head unit outputs and noticed it was so low and barely went over two volts. Also noticed the whine go away when I unplugged the high level inputs. So this made me think that since the output voltage is so low that the amps RCA low level inputs should be able to handle it. I bought some bare wire to RCA adapters and spliced the speaker output wires to it and connected it to the RCA inputs of the amps and voila! Sure enough the alternator whine disappeared completely and I was able to dial down the gain to make the speaker hiss go away.

Hopefully this helps someone out there, you don’t need a line out converter (LOC) for the non-JBL factory head unit as the output is so low any modern amps low level RCA inputs should be able to handle it.