Like many others said, ditch the LOC, and get a headunit installed at the same time as the subs and amp. Run two sets of rcas, (one for sub amp, one for 2/4 channel) that way when you DO upgrade your interior speakers you will have RCAs already ran and wont have to open the dash up again. Also, please PLEASE upgrade your headunit when putting in the subs, your sound quality will improve drastically, even from your stock interior speakers, but primarily the subwoofers. I think its worth it to wait and save the money so you can have that headunit in with the subs. You can probably find a good used headunit for around a 100, or a brand new one for around 200.
edit= dont forget to run your rcas on the opposite side of the power line!!! alternator whine is a drag!