so i have two sound cards on my pc.
one via the on-board sound card.
the other is via HDMI.
so i was intersted to find out if there was a way to assign applications to diffrent sound outputs and a quick google points out this awesome app called CheVolume
unfortunatly this app is not free so a little more googling i found Audio Router which is free.
15/09/18 **Update** Microsoft has announced that they are going to release this feature in an upcoming version of windows 10