REAPER/Mac/Tascam US-2400 setup

[cpd3]

I've searched for and read the threads concerning the US-2400 and still have had no success. It works fine in DP. I've tried all the modes on the US-2400 and created a Mackie Control and two Mackie Extender entries in the Control surfaces/OSC panel with the proper 8 and 16 offsets. REAPER still pays no attention to the Tascam when I move the faders. Is there a toggle I need to hit to make the whole thing work? The USB LED flashes when I move a fader but there's no visual response from REAPER's mixing board.
What am I missing?