“Dolby Digital” would be 5.1 surround sound and Dolby Digital Plus is 7.1 channels but they are different than Dolby Atmos. You can download Dolby Atmos Access App but Dolby for headphones is not free. Instead try Sonic for Headphones Windows 10’s Creators Update also offers a free “Windows Sonic for Headphones” option you can enable instead of Dolby Atmos. Just right-click the speaker icon in your system tray, select “Playback Devices”, click your playback device, and click “Properties”. On the Spatial sound tab, select “Windows Sonic for Headphones”. These are good options to try since basically you are listening to headphones. If your computer has an optical out it might sound better than using the headphone out. Most laptops of course do not have this. You could look for a USB sound card with optical out which will pass Dolby digital to your streamer.
It’s great that your streamer has Dolby Digital because that is what most TVs and cable boxes output of optical cable and without it you would just hear a terrible noise. My TV only gives me a choice of optical or HDMI so I’m not sure how this would work but interested to try.