Hello,
On my PC I can ether have the analog out as default OR the digital out ... to switch from one to the other, I open up the sound application in control panel and in the playback tab I have 2 options - "Speakers" or "Digital Output" since I use both I switch back and forth. Right click and select (SET AS DEFAULT) on the desired output. To further complicate things, when either output is selected I can control the output volume or mute the output entirely, so check those options as well.
Good luck ... every sound card driver is a bit different but if you poke around you should be able to find your settings. It's worth your while to be familiar with them.