Audio interface surround sound problem

Hi,

I am able to get Resolve to recognise and use my Steinberg UR28M audio interface for stereo, though am unable to assign speakers for a surround sound set up. I am only given the choice of two channels when the interface has six.

Is this due to resolve not using Asio and without it the interface can only be used for Stereo? Are there any work arounds if that's the case?

Thanks.