Can I export h.264 mp4 with multiple audio streams?

Hi all.

I've rendered my Premiere Pro video as a Quicktime Pro Res.

In the Export settings / Audio channel Configuration I've created 2 streams.  

Stream 1 = Stereo audio - Source Channels 1-2

Stream 2 = 5.1 audio - Source Channels 3-8

Resulting in a Pro Res QT video with 2 different selectable audio tracks.

So now I'd like to make an h.264 preview of the above mentioned video using Media Encoder,

however when setting the format to h.264 I lose the Audio Channel Configuration tab, I am no longer able to create 2 streams of audio, I have to choose stereo or 5.1.  (and who knows which audio tracks it's going to use to make these!) 

I've successfully created h.264 from the Pro Res master video with both audio "streams" availlable in the final output preview by using Handbrake, so it is possible.

Am I missing a trick here with ME? 

Cheers

J