Int 66 Fn 068E  - IBMsnd Driver - Set Callback Address                     [s]

   AX = 068Eh
   BX:DX -> callback function
       0000h:0000h to disable callback
   DS = value to load into DS when calling the callback function
Desc:  specify the function to be called when playback of a sound effect is
     completed

Note:  the callback function will typically be called during a hardware
     interrupt, so all the usual precautions should be taken except for
     preserving registers

See Also: AX=0691h