Your JBL amp should accept line-level input. I know my 300.1 at least does. Not the greatest option, but it works.
As for the remote turn on... I don't remember what color the wire was, but it's the one that provides power from your tape unit to the cd unit. You should be able to check with a voltmeter.
Actually.. I still have my Mach460 units laying around and maybe have the wiring harnesses still attached. I'll go check and get back to you.
EDIT: I'll have to check in the morning, they're burried under all sorts of stereo equipment right now, and I don't want to make a ton of noise this late at night. Hey, that reminds me, why the hell am I still up at 3:30AM?
JL Audio 12W7, JBL BP300.1
1993 Mercury Capri XR2
1998 Ford Mustang
1989 Audi 100 Quattro
2000 Buick Regal GS