Adding amp to factory system: speaker level inputs?

[Davco]

This is the first time I've used speaker level inputs (usually go RCA cables). Can I tie into the factory sub harness or should I use rear speaker lines?
Also, do I tie in a "remote" cable when using speaker level inputs?

I thought I've read a how to but I can't find it.

[Davco]

Well I found this thread. I'll just pull signal from here.

http://www.mercurymarauder.net/forums/showthread.php?t=8102