Unfortunately the only influence you can have on DTMF is through the 46xx settings file as below , as it points out this is for SIP sets (just letting you know for future ref) , so i would say you need to narrow this down further , you say only certain sets so can you narrow it down to specific ports on the DS module , is the issue actually external and internal calls ...if so again this would point to intrinsic hardware issues on the IPO , as suggested get the unit on the latest firmware , have you upgraded the unit and ds modules from older firmware levels ... if so roll it back to see if the issue follows firmware or hardware , have you got other DS units , if you have swap the expansion port location on the back of the IPO ..see again does it follow the hardware or is the swapped module now having the issue and the other module is ok.
Lots to go off there ...essentially narrow it down as far as you can and come back to us.
##
## DTMF Volume Level
## This parameter specifies the power level of tone, expressed in dBm0.
## The possible values are in the range of -20dBm to -7dBm.
## The default value is -12dBm.
## This parameter is supported on 96xx telephones.
## Note : This setting is applicable for 1603 SIP phones also.
## SET INGRESS_DTMF_VOL_LEVEL -12
##
## CURRENT_CONTENT specifies the URL of an XML file that is used to customize the home screen.
## The default value of the parameter is null.
## This parameter is supported by 96x0 SIP R2.2 and later software releases.
## SET CURRENT_CONTENT "
##
ACSS (UC/SBCE/SM/SME)
Not that they mean a thing anymore , get a brain dump pass the test crash the system.