The most natural sound I've heard from an amplified acoustic was using a Fishman Aura pedal, but they only work if you have a guitar / pickup combination that fits one of the presets.

I'm another who can't bear the sound of piezo pickups. I'd rather have a magnetic pickup like a Sunrise -- they don't sound very natural but at least they sound quite nice in their own way.

The Taylor Expression system is quite effective but I don't think it's possible to retrofit it to guitars.

I'm not usually a fan of miking guitars on stage. It means you can't move around at all, and it's impossible to get any level in the monitors before feedback.