I noticed my amp has an option for speaker level iput in. What exactly is this and if my deck does have it does that mean is has to be connected?

 

well guys.. thnx for all your help.. I now have a second amplifier installed and everything is pretty much running perfect. The only 1 little thing I notice is that now when i fade to the fronts on the deck there is no sound comin from the fronts.. but when i have everything centered and no fading I get all the sound. Is this because im using a second amp and going through that ones rca output instead of the deck? or is it just because im not using the front / rear speaker wire anymore?