Start by making sure you have the latest version of of DP4 (download at motu.com), and the latest OSX drivers for the FW-1884 drivers (download at tascam.com). Recent updates have improved functionality of this combination.

• Once updates are installed, launch the "FW-1884 Manager" found in the Applications folder of your Mac HD.
• On the "Settings" page, set "Control Protocol" to "FW-1884 Native", then quit the FW-1884 Manager.
• Launch Digital Performer and open or create a project.
• From the SETUP menu, choose Configure Audio System >>> Configure Hardware Driver. In the CoreAudio list, locate and click "Tascam FW-1884" so that it is highlighted. Then click OK.
This tells DP4 to use the 1884's audio inputs and outputs.
• Return the SETUP menu, and choose "Open Audio MIDI Setup." In the MIDI page, simply look to verify that the "FW-1884" is automatically detected. You don't need to create or change anything here, as long as the FW-1884 is detected.
• Quit AudioMIDI Setup (AMS).
• Once again, go to the SETUP menu, and choose "Control Surface Setup."
• Click the "+" button to add a control surface. Set the "Driver" to "FW-1884" and "MIDI" to "FW-1884 Control Port, channel 1".
• Click OK in the Control Surface setup window.
• Press the "Computer" button on the upper-right section of the FW-1884 to access the control surface layer.
• Watch DP4's mixing board for faders to respond when you move FW1884 faders; and for FW1884 faders to respond when you move DP4 faders on screen.