I have the same situation. I have a 2011 EX sedan. I want to keep my stock HU, just trying to figure out which OEM wire to use for the amp turn-on wire. I already have an LOC to tap into the rear speakers, so I can run my sub and amp.
mild hijack in progress.....I was thinking about upgrading my amps (alpine-comps/mtx-subs) and saw that the JL amps have something called signal sensing and don't require a remote turn on wire. I thought that was kinda of cool. I wonder if it works.