I've done a lot of research with this, an I have made a custom system for my Tacoma that is loosely based on the K&K system. The K&K Trinity system is the finest available today. You have a
condenser mic blended with body transducers. No undersaddle pickup, and no preamp in the guitar, so no holes besides the output jack, and there's an outboard preamp/blender. If you are after Michael Hedges purity, then you need the mini condenser. I couldn't bring myself to buy the GHS or Fishman system after hearing the K&K system. Nobody does natural acoustic sound better. They are at
www.kksound.com.
My Tacoma is a piezo and a shure mini condenser mic, and then I made my own outboard preamp that either splits or blends the two. I used the same mic and a different piezo in a classical I made, but I use the same outboard preamp. Neither guitar has a battery. Everything including the phantom power for the mic is outboard. It cost me far less, so it was worth it, otherwise I would have gotten the trinity system.