Yeah, those should have many audio tracks, the first three being DTS-HD MA (#1 being 5.1, #2 being 2.0, #3 being mono). Don’t know why you’re not seeing the different tracks in VLC, they should definitely all be there.

Are you bitstreaming the audio without reencoding it to your receiver (that is, sending the raw DTS data instead of letting VLC or your Mac convert it to PCM or something else first)?

Might be a Thunderbolt or Thunderbolt to HDMI issue, I’m not sure. Haven’t had a Mac in years, and when I did it was pre-Thunderbolt.