When I play MKV or M2TS files that have multiple audio tracks, on my PS3, I can't seem to figure out how to change the audio track. On the PS3 controller I will press the triangle and go to the audio icon (looks like a musical note), but it does nothing.

I can change audio tracks with my WD TV Live Plus'es, but not the PS3. I tried searching the site but couldn't find anything on this but I'd wager it's common/simple/straightforward and I'm just clueless.