Help with sound system

Hey yall, i have an 02 ford focus and im putting in subwoofers. I have a stock head unit and plan to keep it. I need to know how to hook up the r.e.m. cable to the stock head unit. thanks for your help.

i've never heared of that being done

I agree with ZX2. I put in a new head unit about a month ago...there are no extra inputs/outputs of any kind on the back of the stock, only the plug for the harness. Do yourself a favor and buy a good aftermarket headunit..make it much easier to hookup, plus to stock head unit more or less sucks compared to aftermarket units. I heard things with my new H.U. that I'd never heard before on my CD's, with stock speakers.