Kevin,
I found this on Datheads:
From: Todd Romero <todd@routeflap.net>
Subject: GP DMIC-20 mod
Date: Fri, 25 Oct 2002 18:34:58 -0400 (EDT)
if anyone is interested in having a gain mod done to the dmic-20 drop me an email. this will add pots to the faceplate that will give you trim
control between the 5 db dip switches. also, after some discussions with GP they are considering adding this control to future production. in the mean time, ill do this mod for $100 for any interested folks.
see pics here:
http://www.routeflap.net/dmic20/Hope this helps,
Drew