I just mounted my ROTR BD image and opened it in Media Player Classic.
6 channels, it says.
JEDIT:
Okay, I don’t know if this is Audacity’s fault but I got the same result.
I ran the M2TS from my BD image through tsMuxer and demuxed the AC3, then loaded it in Audacity.
It makes me want to check other software to make sure it isn’t Audacity goofing up.