Multichannel audio on SDI - not working

I've searched through this forum and google and just simply can't find a solution how to enable multichannel audio playback on SDI.
I'm using Caspar f15ba60 Beta 2 with Blackmagic Decklink 4K Extreme 12G (driver version 10.8.5).

The test file I'm working on is a simple 5.1 WAV audio file. Link to this file:

I also don't clearly understand how to use the channel mappings, for example to polay a stereo file on (for example) channels 7-8 in SDI stream. I tried every configuration of the producer usinf channel layouts and also played the wav file using additional channel)layout command but I get every time only stereo 2 channels output (downmixed or just 2 channels).

Could someone give me a hint?