The DM4800 needs to be connected via USB to the computer.
On the DM4800:
Go to Remote>Ext.CTRL screen and add a 24 HUI Emulate.
Go to Remote>Machine.CTRL screen and add an M HUI Emulate and enable the TRA button.
Go to the Setup menu>Peripherals>MIDI Controllers.
Set Type for #1, 2 and 3 to HUI.
Set the Receive From and Send To for each HUI to the corresponding Control port on the DM4800. (On Mac OS, those will be Control port 1, 2, and 3. On Windows, they’ll be Ports 5, 6, and 7.
The transport on the DM4800 should work all the time. The Faders and other functions work when the Layer Status on the board, to the right of the Stereo fader, is set to Remote.