prg 204-06" (What does that mean ?)
That is the option to have the OCA come out of the speaker or the handset.
So do you have the FB38 unticked in the COS for the handsets that are receiving the OCA?
Do you have the FB32 and FB33 set to Disable or Enable in P200 Station Data for the handsets performing the OCA
You could also change the Card Slot Assignment to "BDKU or BWDKU - 8 or 16 DKT without Spkr OCA" this will disable the feature for those digital handsets connected to the card.
The last option is to remove the BVSU module from the DKT handset.