so with the Alpine amp you would just use spliced RCAs to connect to the amp?

do you tap into the front speakers or rear speakers for the signal? does it make a difference?

 

Yes, if the amp has differential inputs you can just splice RCA's directly. Front or rear does not matter, choice is up to you.

More than just Alpine and JL have differential inputs. Off the top of my head, I know certain Rockford Fosgates have differential inputs, along with Zapco.