Thanks for the pictures AustinKnight. It looks like the damper is a simple choke that restricts air-flow by making the intake opening smaller. I'll play around with my setup to see if I can restrict the flow from somewhere other than the ball valve.
The software is set up with a max blower speed. I'll try reducing the speed so it's not blowing in too much air. I had it on max because it was forcing air through the half-closed ball valve.