Right now I've got a Kenwood MPV-7019 head unit with a pair of Infinity Kappa 6.5" coaxials being powered by a sony 80W x 2 RMS amp. I'm looking to upgrade the rear 6 x 9's and add a sub next. I'm probably going to get the Rockford Fosgate Power 851X amp 110 x 4 RMS, and Infinity Reference 6 x 9 3 way 100W RMS speakers. Next, I'm thinking about bridging the final two channels to get about 220W RMS power into 1 channel at 4 ohms. What sub would you recommend to complete the package? If I got a dual voice coil sub, could I wire it to present a 2 ohm load to the amp and get 440W RMS power? Would it be safe to do this and could the amp handle it? Secondly, I'm looking at a 4 gauge amp kit for all of this and my main question is how many RCA's am I going to need because I could save around $30 going with a kit that only includes one rca. Ideally, I'd want the Rockford passing the signal to the sony through the preamp output (I think?) because the Rockford's a better overall amp. What all am I going to need to do this and are two RCA's going to be necessary? One last question, I know I'm going to need a 60 amp fuse for this what does that mean and is an 80 amp fuse better or worse? What do the numbers mean? Any help is appreciated thanks.