FYI, I ended up putting in an Odyssey 34/78 AGM battery in the 2nd location near the passenger firewall. That thing is a beast.
I've separated all my audio electrical from the truck's system (except the headunit) and all my electrical troubles are gone. Love it. I've got 3 alts, one stock 145A to run the truck, an Ohio Generator 300A unit for the system, and a dead placeholder in spot #3. I was planning on a 2nd high output alt, but as of now, I don't really need it, so I'm just chilling with 2 functioning at the moment.
For those who are running high-wattage sound systems, I can't recommend Ohio Gen enough. Don't bother with the "bargain" alts you see on Ebay and such - there's a reason they are cheaper - they're not built to the same standards. I went through a number of cheaper alts, including running 3 remanufactured stock alts with a multiple alternator control unit, always had problems, questions of if they were working right, etc. Finally just went all-in with the totally separated electrical system for my audio and everything is copacetic.
<edit> BTW, running about... mmmm... 7400 watts, I think. Of
true, solid, clean Zapco power.