OK!!!
First, let me apologize for taking so long with an answer. Ok - here ya go:
1. Just like Jarno said: "
MIDI/CtrlChg MIX/MASTER/FADER/ST -make sure "USB: 4" is connected in MIDI/SETUP. So you were able to get that to happen.
2. In DP - maker sure that your MIDI IN - is set to TASCAM DM USB-4
3. In DP - maker sure that your MIDI OUT (on that midi track you have designated for the master fader data - is set to TASCAM DM USB-4 also - it needs to know where to send the controller data to. Also make sure the midi channels on the midi track in DP match the midi channel you designated in the DM (i.e. MIDI Ch. 1, Ctrl. #7).
4. Go to Layer #1, and hit play in DP. If you are in the Remote Layer - you will not see any movement on the DM's stereo fader. You have to be in one of the first three layers to see the stereo fader actually move.
This works in Cubase 6.07 and I have to admit is quite the useful tool.
I'm sure you'll dig it - took me all of 5 minutes to get it to work. It scared me a little when I saw the stereo fader actually move.