I see that you were in the other thread here...
http://www.myrav4ev.com/forum/viewtopic.php?f=9&t=1303
I started to do what LastEmp did and purchased a Cleansweep, and I still have some old skool Soundstream amps that I'm going to run. I still haven't setup the system yet. Just so busy.
But from what everyone has said in that other thread, there is no dedicated "line-level" output to a stock OEM amp. So you have to use an inline digital processor (like the CS) and then you get your RCA outputs, etc.
Plus I've heard that if you try and upgrade the OEM speakers... it can be a real pill... because they are tuned to the headunit.