its exaclty what it says. you take the speaker lines coming out of the radio and hook them to the convertor. RCA's are only 2 wires for a speaker connected to a jack for easy connections. split the line, and install the converter use the rear right and left. your wire will still go to the speakers, but it will also send the same signal back to your amp/subs.
yes you can also take the signal from the rear speakers. and regardless of what way you connect to the speakers, youll have to run a remote turn on from an acc turn on from in the car. (something that turns on when you turn the key). run the wire the same time you run power to the amp.
if this is too hard, go to best buy or circuit city and have them install the amp for ya for a couple bucks. as far as the dash coming apart,
http://www.8thcivic.com/forums/showthread.php?t=3534
have fun.