[panhandler62]

From also reading your other thread on this issue:

I think you should start by making the changes to the starter circuit that VetteVet suggested, then, once the starter circuit is functioning properly, revisit the stereo.

I think your links got mangled when you copied the info here so they all result in "no finds" but, unless you are going pretty extreme on the amps you can probably get by on the stock charging system (though things may be iffy at idle.)

I would run an appropriate sized lead from the junction box, heavy enough to supply both amps, and use a bus splitter to supply each. Ground each separately and make sure your cab to chassis ground is buff enough to handle the load.

There is no way an alternator upgrade is a *bad* thing, but if you're not having charging problems (or 4 watt headlights at idle!) then it's not an absolute requirement.

A separate/dedicated battery is also a nice upgrade, but superfluous on most systems. It's always good to balance upgrades with need since most of us are not made of money.