Nvidia Shield surround sound (UK)

I'm currently trialing Channels and I'm having a bit of trouble getting the surround sound working how I want it. Having a read through the forum, I gather that most broadcasts in the UK only have two channel audio.

When I use the HDHomeRun or Live Channels app, my amp receives audio as two channel Dolby Digital.
When I use the Channels app, my amp receives audio as two channel PCM.

I have my amp configured so that when it receives two channel Dolby Digital, it uses Dolby Surround to upmix to 5.1.

I could configure my amp to do the same when it receives two channel PCM, however this would mean that when I use the Spotify app on the Shield to play music (which the amp also receives as two channel PCM), this would get upmixed to 5.1 too, which I don't want.

Is there any way to get the Channels app to send Dolby Digital instead of PCM?

Thanks

Location: UK
HDHomeRun: HDHR5-4DT
Shield: P2897 (2017, non-Pro)
Amp: Denon AVR-X2300W