techsafe

We have a 16 camera system installed in the 90's. 5 of the cameras have PTZ and several have zoom function. The camera's are Burle. Camera feed into a multiplexer and loop through to another unit I think is a controller which is connected to a key board with joystick. The keyboard allows the operator to select cameras on the monitor and control PTZ functions. Currently the TL VCR requires replacement and the multiplexer is not outputting signal for 2 of the cameras. We would like to upgrade to a DVR but want to know if we will loose PTZ control because we do not know the protocol of the devices. Is it possible to just loop through the DVR as is currently done with the multiplexer to the controller? An installer suggested this. Are these older PTZ cameras only able to be controlled through their own controller or do they actually have a protocol that can work though a DVR? Any help on this wouldl be greatly appreciated. I would like to know if and how this will play out before spending money on the system. Thank you