Hi,
You probably (hopefully) found your answer by now, but in case other people find this thread, I thought I'd share a few things... Premiere is a little odd in the way it handles audio, at least that's my pov. The way I've got things to work when exporting MXF Op1a, which I do regurlarly when exporting for local broadcast stations, is to set the audio tracks when creating a new timeline (I now have a preset I can use anytime I need a new track). When creating the track I creat 8 mono tracks and attribute them 1 and 2 to 1&2 ouputs, 3 and 4 to 4&4 outpus and so on for the 8 tracks our local broacast station sks for. Then if I receive stereo tracks, before importing them to the timeline, I do a right click on the medis file and modify the audio form stero to two mono tracks and attribute the left to 1 and the right to 2.
If your timeline is setup this way, you should then have the option to attribute 8 mono tracks in your export settings.
One more thing, I forget, I'm not in front of Premere right now, you may also need to set the left and right PAN of ean track in the audio track settings, at least to hear thing more or less the right way.
As to VLC, it is a grreat software, becasue it just finds ways to read file however which way they were made, and because of this, it is in no way relevant to check you files because it will workaround metadata and errors to try and make the file work.
Cheers