I think I am going to do this with an under bridge piezo. The first guitar I saw this on was a Duesenberg Sessionman that they made for Tom Bukovac and the tonal palate on that guitar is great. But as we all know, tone comes from the player more than the instrument and Tom is up near the top of the list. Still it would be fun to try this and I think the under bridge is the way to go for me. Everything in your reply was valuable! I may go as high as a 1m pot. I can always drop back to a 500k if I don't like it.

Now, every guitar I have had, mainly acoustics, that had an under bridge piezo were also active so I also have to think about where to put a 9v battery.