With a name like Landry, you are from over here!
Don't worry--I'll consume enough crawfish and beer for you this weekend!
Anyway, I'd use the high level outputs of that Sony Radio, unless you want to use the sub control in the head unit.
In that case, what you need is an "Adjustable Ground Loop Isoloater" It has RCA in and RCA out, and level controls on it...
Search for one made by PIE, or AAMP.
Bazooka Mobile Audio