M-Audio Fast Track Pro

Problem: even though outputs 1&2 as well as outputs 3&4 are selected, audio is not received by both amplifiers.

Control Panel
+---Sounds and Audio Devices
    +---Audio
        "Sound and Playback Devices"
           Fast Track Pro Out 1/2
           RealTek HD (or whatever onboard)
           Fast Track Pro Out 3/4

and in the M-Audio U/I

How does the user select both 1/2 and 3/4 so sound goes out all channels (necessary for L&R amp 1 and L&R amp 2 ?

There is currently no known solution. It seems to be a limitation.

Workaround: connect the second amp to the headphone out on the front of the M-Audio Fast Track Pro. Make sure A/B button is OUT.