Exporting multiple audio channels from Premiere Pro CS6 in MXF OP1a

I have a Premiere Pro project with multiple audio channels and I want to export them as individual channels in a MXF-file.

Method:

When I created a new sequence I choose "Multichannel" from the "Tracks" page. When I export the MXF OP1a, I choose 8 channels from the "Audio" page. I make sure that none of the channels are muted.

Result:

The rendered file contains 8 channels as I want it to, but only the first two channels contains audio (main left + right), the rest of the channels are empty. Channel 1 and 2 contains the audio from all channels, but I want the channels to be seperated in the same way as they are layered in Premiere.

Any ideas what I can do?

Thank you for your help!