Yeah, I figured out its a voltage drop. The lights would get enough current, just not enough voltage. As for a cap... usually the can help with very minor light dimming, but if your lights dim alot and for a long period of time, they aren't going to help. They are definitely not going to save an alternator if the current draw is too much either. I would wait until you install everything to see how bad it is, and if its not too bad you could try a cap and it should help some.

As for the fuse sizes... like I said earlier, your fuse size first and foremost depends on wire size. The 'upper limit' to your fuse size depends on how much current the wire can carry. For example, you would NEVER put a 150 amp fuse on 4 gauge wire. 4 gauge can only carry around 125 amps safely, so a 150 amp fuse would be pointless. So, pick your wire size first, according to your current draw, then pick your fuse size. For the sub amp, your maximum draw would be 40 amps. So, the correct wire size would be at least 8 awg. (can safely carry up to 50 amps, so your fuse rating would need to be between 40 amps and 50 amps). For the multichannel amp, your max draw is 50 amps, so you would need to use at least a 6 gauge wire (can safely hold 80 amps). Therefore, your fuse on that wire would need to be between 60 amps and 80 amps. Get the picture?