buying an amp kit is cheaper. I bought my 4 gauge kit from
www.knukonceptz.com
The Kolossus 4 gauge kit is the best you can get for the money.
I would just mount the highs amp in the back next to the sub amp...easier.
You just need a distro block with 4 gauge in and two 8 gauge outs. For the short run from the block to the amp 8 gauge will do fine. Just make sure you have a 4 gauge ground for the sub amp.