18 xxx how to wire two batteries and amp

2003 Nissan Pathfinder LE 

Okay, I just replaced my oem alternator last weekend with a HO 220amp alternator and upgraded the big 3. I also bought two new batteries that are identical. I have not installed subs or speakers yet.  I have a re audio 18"XXX sub that is going to be powered by us amps ax-3200de and MB Quart  RVF and RUA 216 speakers that will be powered by us amps merlin MD41 amp. My question is how to wire this. I wanted to use the third diagram on this page, but I am not an expert and am confused about what is going on (what size wires I should be running and where to find a fused dist. box like the one in the pic) :  https://www.bcae1.com/battiso.htm

I would assume 0 GA from front battery to dist block and 0 GA from back battery to dist. block, but do I need to use 0GA for an amp this big that is pushing 2000watts? Would the power for the sub amp be hooked to the dist. block or directly off the second battery? Any detailed help would be great. I have had this stuff all summer and finally found time to install.

THanks

Use this guide to determine what size wiring and fusing you'll need. Trust me, there are enough sources on this site! Cheers!

https://www.the12volt.com/info/recwirsz.asp