It looks like there is a trigger input on the EP600, but I can find no mention of it being functional. Is there any way to operated the EP600 in triggered mode?

Yes. I highly recommend calling Axiom for details, though, as it's not well documented.

The trigger input on the EP600 allows you to remotely power the sub off/on.

Dennis! Long time, no see! Hope things are happy with you and yours.