I recently added a Markley Pro-Mag humbucker to my equipment list. While it *does* amplify the guitar, it actually only amplifies the strings.... as it should, naturally. It still sounds sorta acoustic; but lacks the resonance and tone I was looking for.

I know there are microphonic PUs out there that either are fitted onto or drop into the body. My question is; will that sort actually sound more "acoustic" ???
Sure... mic'ing up a session may be what most will say; but that option leaves you pretty much staged at an exact position. Move of the "X" and sound will suffer.

Anyone use/ever try a "drop-in"????? Brand or type? Piezo, dynamic, condenser, cardoid??

A guy that comes into the store I work at swears by the L. R. Baggs Anthem. It has a piezo pickup underneath the saddle, as well as a condenser mic that is secured to the bridge plate. There are some controls so that you can blend between the two pickups to give you a really impressive sound. I've only heard it twice, but both times I was fairly impressed.

I have the M1 Active, also by L. R. Baggs, in my guitar right now. It works as well as I could hope for it too, and I tend to get a compliment or two on my sound quality when I make the rounds at the open mics. It's similar to what you have, but it also picks up the vibration of the top of the guitar.

The last one that I'd like to try is the Seymour Duncan Mag Mic. It's the same idea as the M1, but there is a blend control to mess with the balance between the sound picked up by the posts and the sound it captures from the top vibrating. Maybe someone else can give a bit more insight, as I haven't gotten to play around with one yet. Though I do know that it's what Ben Harper uses in his live stuff.

Only thing I can really say for sure is that any one of the pickups I mention is going to cost you in the realm of $180+ brand new. They are expensive, but they provide a quality sound.
"Here I sit, beneath a lonely line."

~iband48's signature
The setup described by iband above is generally thought of as optimal. Used to be such things were only available as custom items.
Good under-saddle piezos are likely the second-best.