System Configuration : System Setup : Configuring Avid HDX, Pro Tools|HD, and HD Native Hardware Settings : Routing a Pro Tools Output Pair to Multiple Destinations

Routing a Pro Tools Output Pair to Multiple Destinations
Pro Tools channel pairs can be routed to multiple physical outputs on an audio interface through the Hardware Setup.
For example, if you assign Channels 1–2 to both outputs Analog 1–2 and Analog 3–4, when you send a signal to Pro Tools Channels 1–2, that signal will be routed simultaneously to both pairs of output ports on your audio interface.
This lets you send the same signal (such as a stereo pair, a stem mix, or a multichannel mix) to multiple destinations (such as multiple mastering devices).
To route a Pro Tools output channel pair to multiple audio interface output ports:
1 Choose Setup > Hardware.
2 From the Peripherals list, select an interface.
3 Click the Main tab.
4 Select an output port pair from an Output pop-up menu.
5 Control-click (Mac) or Start-click (Windows) the same pop-up menu a second time to choose another available Output Port pair.
The output name updates with a plus sign (“+”) before it to indicate that multiple output ports are selected. In the pop-up menu, each physical port pair assigned to that Pro Tools output pair is indicated by a check mark.
6 Repeat the above steps to select additional output destinations. The only limit to output choices is the number of outputs available in your system.
Pro Tools output pairs can also be routed to multiple audio interface outputs in the I/O Setup. For more information, see Configuring Hardware in I/O Setup.