PulseAudio - No output when using multichannel sound card

Steps to reproduce:

1. Connect an external multichannel sound card (for example the Focusrite Scarlett 18i20 with 10 output channels) to the PC
2. Play an audio file or a video with an audio track with QMediaPlayer

Expected:

• Audio plays normally

Actual:

•  Audio is essentially inaudible, metering of output shows low signal.

Notes:

• PulseAudio reports the sink channel map to include front/rear/side pairs + front-center + LFE + 2 AUX channels.
• QPulseAudioInternal::channelConfigFromMap returns 7.1 surround channel config for device
• The PulseAudio default channel map is set to only front left/right pair.