HDMI Audio not being passed to amp

[Shadows1990]

Hi all.
My problem lies with passing audio from my HDMI port on my laptop, to my Onkyo 507 amp when playing a game.
The audio gets passed through absolutely fine when playing music, a film and anything which doesn't require a resolution change. As soon as I launch a game that starts in a resolution that isn't the desktop resolution (1080p), the audio is not passed to the amp, and plays through the laptop's internal sound card.

I've tried changing drivers, disabling all other sound devices, and tried changing some codec packs.
Does anybody know what's going on?

 

[Shadows1990]

Ok, so I might have a temporary workaround.

If I change the resolution to the one I want to use (for example, 720p) on the desktop, there seems to be a different 'Nvidia HDMI Out' device, which doesn't have the settings I've set-up when in 1080p.
If I change this to be the default while still in 720p, whenever I switch to that resolution, the device will be used.

It seems really odd that this is required, as I don't remember having to do this before?
Like I said, I've tried multiple display drivers as well as HDMI audio drivers, all with the same problem.