From the QLab website:

QLab can access all audio channels within the first audio track of your video. This can be confusing, since the words "channel" and "track" are often used interchangeably. In the world of video files, one video can contain multiple tracks, and each track can contain up to sixteen channels. When a video is prepared for DVD production, the first track might represent the 5.1 surround mix, and thus contain six channels. The second track could be an alternate stereo mixdown, and thus contain two channels. Since QLab can only access the first track of a video's audio content, it's important to keep these differences in mind when preparing your video files.

This means we need to stick to a single audio track with multiple channels. This guide shows how to set this up in Adobe Premiere.

First, the sequence must be set up correctly in Premiere. Use the following settings under "Tracks" in the sequence settings:

Track settings

Output assignment

Breading

See and example with the above settings.

Export

Select Quicktime and e.g. ProRes LT with the following settings:

Also remember to change "Channel Layout" to Discrete.

See and example with the above settings.

You may want to see this Youtube guide which explains the above, but remember to select Channel layout: Discrete when exporting - otherwise QLab cannot recognize more than one or two channels.