My friend Tod and I are intending to hook up is Rio Car to a similar Dodge Durango factory Infinity amplifier.

As I understand it, it needs a slight boost before going into the amp, and there is a product by Pacific Accessory Corporation called the "OEM-1" that supposedly will handle this exact situation for us. We have not received it yet so we can't report on its success yet. But I intend to get photos and do a full write-up once we get it in there.

The OEM-1 is mentioned and linked in the FAQ. It is sold mail-order by www.tune-town.com . Perhaps this is what you need, as well?