multiple battery audio system

I currently have a Mechman 370a alternator charging 5 XS power batteries, 1 D6500 under the hood and 4 D3100s in the back. Wiring under the hood, have 0ga power from alternator positive post to the battery positive, 2 0ga grounds from an alternator mounting bolt; one directly to the front battery negative and one directly to the frame along with a 0ga coming from the battery and the factory ground. There are 2 0ga positive wire from the front battery to the back into separate 400a fuses about 3 feet from the 4 batteries/bank from there to the bank. Have 2 0ga ground coming from the frame directly into the bank. I have a volt meter in the vehicle but it runs off of the 12v charger leads, and typically it runs and stays at or above 14.3

A few weeks ago I experienced some issues with the music, checked thru the system and found there were some blown fuses from the front battery going back and that some of the ground jump leads in the back had apparently overheated and started exposing wire. At this point, tested the rear batteries and they were very low voltage. We removed and replaced the damaged wire, doubled up the ground jumper wire. Later on and over the next few days I slow charged the batteries, but connected it from the from battery under the hood. Left it charging for about 24 hours over the course of 2 days until the green light indicated it was full. I am still running into issues when the bass drops and the voltage drops to 13.8- 13.9 or will send the bass amp into protection.

Any suggestions on what the problem could be?

This is a setup in a 2006 Dodge Ram 1500, running an HCCA 8000D and 2 Hertz HCDP4 amps

Copper, or copper clad aluminum wire? Soldered connections?

All OFC wiring throughout the truck, connections are crimped, however not soldered.