Volume limits on driverack 260

I have a driverack 260(DR260) with 3-4 of the ZC-2 zone controllers. The DR260 was installed around 12-13 yrs ago and also has been sent in for service once and reinstalled. The problem I'm having is the ZC-2 controllers have been going bad and one of them only has a limit that either I don't know how to change or something...it only allows me to decrease the volume to 4 then it automatically mutes the zone. We just revamped the sound system to a point. The techs that installed the new equipment said there was a problem with the dbx because they thot the output volume was way too low. Do you all have a solution for this problem or is there a new and improved version of the DR260 or what is my best route to go? Those ZC-2 controllers are $200-$250 and to be replacing them gets a little costly. Please help!! Thanks!!