I have a Plugable USB 3.0 Docking Station connected to a Dell G5 15. I connected to the microphone plug of the station Logitech Surround Sound Speakers Z506. Surround sound does NOT work. Just stereo.
I am running Windows 10 Professional, latest build, all drivers updated. If I go to the Sound Control Panel, Playback tab, I select «Speakers, Plugable Audio» and click on Configure, I see two options: Stereo and 5.1 Surround.
If I press Test button when Stereo is set, it works fine for from speakers. If I press Test button when 5.1 Surround is set, all speakers in graphics show when they are tested, but sound is audible only for fron speakers. Please, note that if I press Next when 5.1 Surround is set, Center, Subwoofer and Rear pair are checked as expected, so they should work.
My impression based on your description is that you are using a Plugable UD-3900 docking station → https://plugable.com/products/ud-3900 Please feel free to correct me if I am mistaken.
Presuming for the moment that my understanding is indeed correct, the 3.5mm analog audio output jack located on the front of the UD-3900 supports 2-channel stereo output. The UD-3900 does not support 5.1 Surround Sound audio output.