Get a small mixer with 2 prefader aux-busses. It's only 2 guys playing acoustic, so i reckon its only four mic's...right? (2 vocal and 2 guitar) Then you dont need a very large console with a slew of micpre's.
Get one with more then enough pre's (5 or 6 or so), end get 2 powered monitors (wedge with amp build in).
idea for
mixer
idea for
monitors
Or.....just learn to live with a less then optimal monitormix for you (ie.....use what you have now and dont change a thing...)