line level output?

Howdy. I have a 1989 Buick Reatta. These things don't have a "head unit" but radio functions are controlled by a touch screen CRT, which in turn controls a radio module, and then sends audio out to the speakers. Speakers are round 6.5'' in the rear and 5.25s in the front. I would like to upgrade my audio system, which includes adding a small 4 channel amplifier. I'll be using a high end amp and speakers. How can I get RCA output from the Reatta's "Electronic Control Center" radio module? I once heard of something called the JL Cleansweep, and it sounds like that's what I need, but isn't that not in production yet? Can someone please explain what my situation is, and what I need, along with examples of such products? Thank you.

I checked Crutchfield and found the Audiolink Powerlink II. It looks like this is what I need. Is this a high quality unit? I ask because of my really high end quality amp and speakers I want to be running. Thanks.

And another thing... For this unit, it looks like I'm going to need two because it only supports two channels. So for 4 channels, I'll need two. But I just said that, ooops. How do I "merge" these 4 channels together into an RCA signal into a 4 channel amp?