A component video cable is just a set of RCA cables (albeit, a set of three of them). Use the RCA. Odds are, you won't even hear a difference, unless you are using crappy cables. If you use the component, just plug the same color from the amp to the sub (you only need one single RCA). You only need to plug it into the LFE input on the sub (shooting from memory here, on the road).  

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Scottiemon