Via the Audio button on the remote control, not through the Audio menu option of the disc.
However, I will make a couple amendments to my statement:
1. The first track is silent for the first minute, no matter if you are using PCM or DTS on this disc. Switching between DTS and PCM during this stage will show changes on the OSD and front panel of the player, but there is no audio acquisition on my receivers (verified with digital coaxial and optical to PIoneer Elite VSX-54TXH and HDMI to Integra DTC-9.8).
2. I redid my tests, and the breaks I was having with losing the DTS track when changing chapters was due to a handshaking problem with the projector. I disconnected the projector from the chain and no longer have the problem. I will trouble shoot this problem tomorrow night when I have time to swap out cables, mess with resolutions and timings on the VP50.