Hi - all my banjos (26) have at some time been used in a band and with a range of devices to amplify them. Overall I agree that one of the main problems is maintaining a banjo ,sound and this is best achieved using a good microphone. I also have a system fitted to one banjo which consists of what I would call a Drum Head Mike fitted very close to the inside of the banjo head. Works fine in a single instrument setting but loses a lot when used in a full PA rig.
One of the best bits of kit I have is a simple stick on mike on the front of the banjo head. (Cost the princely sum of £2 in a local charity shop)
Hope this is of use.
Keep Plucking
Pete
PS Pigs are very clean sweet smelling creature if they are looked after in the right conditions.