I don't like rear speaker, so Im going to say cheap coax. I had great luck with Blaupunkt PCxts when I first got my car. They'll run you about $35.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>