I too have the "premium hifi" system which is the standard system on our cars for '08-'09. I am running the JL 500/1 with the 10" JL W6 subwoofer.
1) I did use a LOC for the signal. I believe you are correct about the JL amp, but I did wire up mine using the LOC.
2) I first tried without a remote wire but was not able to get it to work. I ended up running a quick wire from the accessory slot in the fusebox behind the glovebox and ran that to the trunk.
3) Wiring between the logic & our standard system will be different. There's alot of threads both on here & also e90post about wiring. This thread will help with the wiring for our vehicles
http://www.e90post.com/forums/showthread.php?t=87130 .
4) If Technic has the pre-spliced connectors available for non logic cars, that's the way to go. Very clean way of doing it. The other option is to use taps.