Can someone help me to understand whats needed for a dual amp setup?

I have a 4 channel amp w/ DSP I will be connecting from the factory Headunit. That amp has a signal preout which I like for a future powered sub. This 4 channel amp also requires a 4 gauge power wire.

After looking at some of the 4 gauge dual amp kits for sale, they all carry a long length of 4gauge of power wire and a smaller length of the 4g for the ground. It also comes with the distribution block. Now I believe I understand the basics of the kit: 4 gauge length from the battery --> fuse --> 4 gauge length --> distribution block --> split to 4 channel amp and powered sub amp.

What confused me is that most of these kits come with an additional 8 gauge power and ground cable. Whats it for? It's smaller than what the 4 channel amp requires so I can't use it. If my future powered sub requires a 4 gauge wire, it can't use it either.

Any help?

 

Link?

You wouldn’t need a 4 gauge from the distribution block to the second amp if it was not far away and/or lower output. I ran a 4 from battery to block. Then 4 from block to my large 4ch and 8 from block to my smaller 2ch. Really depends on outputs and run length.

 

You have the right idea. Some people can also run:
battery - 4ga - fuse- 4g - distribution block - (4g - fuse - amp 1) and (4g - fuse - amp 2).

Be careful about the dual amp wire kits. If it's 4ga copper clad aluminum wire vs oxygen free copper. Spend the extra money on the latter.

How much power for the amps do you intend to use?