How do I get Stereo + 5.1 for YouTube videos? Youtube states that it only supports Stereo or Stereo + 5.1. 

How does this work? Does it mean that there should be two audio streams included in the container or is this a special encoding?

( I am using Premiere Pro )
It's not very clear what they mean. If you look further down on the same page it says it accepts 5.1 @ 512 kbps.

Recommended audio bitrates for uploads

Mono    128 kbps
Stereo  384 kbps
5.1     512 kbps


YouTube doesn't currently support 5.1 playback. If you upload a 5.1 audio track it gets converted to stereo.