Need help with wiring up acoustic internal mic and piezo preamp

[Jabulani Jonny]

I just recently picked up a Rane AP13 acoustic preamp, which actually came with an AKG gooseneck internal mic for acoustic guitar. I'm currently playing an Alvarez Yairi WY-1 that I've had since '97, and I love it. I'm pretty handy with a soldering iron and I'm considering installing the mic via Dual Lock or mounting a small wood block to attach it to inside the guitar. At any rate, currently the guitar sports a typical under-saddle piezo pickup and battery powered preamp. So I'm guessing the current wiring is hot signal from piezo to tip of TRS output jack, battery negative to ring and ground from piezo and battery to sleeve. Does that sound right?

I'd like to incorporate the internal mic and the Rane AP13 allows for TRS input, with tip from hot piezo, ring from hot mic and sleeve being ground. However, how do I wire this up with my existing battery powered preamp setup? I would assume that I still want the preamp to only power on when a cable is plugged into the jack, but I can't figure out how to make that work if I use the ring from the TRS for the mic hot signal.

Any thoughts and insight is much appreciated. Thanks!

Jonathan