"Steam Streaming Speakers" only shows 5.1 setup with side speakers

[SixelAlexiS]

As the title say, I can only select a 5.1 setup with side speakers instead of rear speakers.
With my audio drivers I can select the 5.1 with rear speakers without issues.

Is there any way to force the 5.1 rear speakers setup on "Steam Streaming Speakers"? Thanks.