Ah jeez, I pulled the factory head unit out today and it quickly became tricky.
Because it's the top of the line factory unit it has a separate amp and that is connected to the head unit with a circular, multi-pin, "din" connector. That's the 6 pin connector. And there is also an 8 pin connector that seems to not do much in my car.
Hopefully, all I need to do is make a custom connector that goes from the 6 pin DIN connector to 4 male RCA's and I will just bypass the amp on the new head unit. Which is a bit of waste, but never mind.
I've been deep into the interwebs trying to find pin-out diagrams and message board how-tos.
And I've ordered the 6 pin and RCA connectors from Ali. We will see how it goes
yeah, Tortron, bypassing the factory amp was my first idea, but the advice I got was that the factory speakers would sound like crap without it