Digger, your choices depend on the situations you need the gear for. I assume you are looking for more runtimes. The din-3 plug is a great idea as you can get cable to run Tekkeons, 9V DVD or RC batteries, and have the dual battery tray for lighter uses.
The PMD-661 is a beast on its own, and my vote is for a battery system that will NEVER send voltage more than 5v.