Another way is to use the latest version of Audacity. It can export 5.1 channel audio in a number of CODECs, including PCM (.WAV). You have to enable this on the Edit->Preferences->Import/Export dialog. Once that's turned on, when you export to a file it will display a track to channel mapping dialog. For both AC3 and PCM the channel mapping is:
1 -> Left Front
2 -> Right Front
3 -> Center
4 -> LFE
5 -> Left Rear
6 -> Right Rear
You should be able to import this into the authoring app. Please note that you require an optional library for AC3 support. I'd try the .WAV file first just to see what happens. I'm still playing around with multi-channel output in Audacity myself, so I can't make guarantees.