Thanks for posting. Unfortunately I don’t expect this issue to be easily solvable.
For several years, PC & sound card manufacturers were implementing the option of digital audio through 1/8"/3.5mm audio jacks, which previously had always been analog only. This implementation never seemed to fully catch on, and I haven’t seen a sound card or new audio output device in many years which supports this. (And I’ve done some looking awhile back, as I have a nice set of Boston Acoustic speakers which are unusable without this type of jack.)
The HDMI port provides digital audio output, but for your needs you’d need some type of in-line widget to plug in between your dock and the monitor which would break out the audio portion of the signal and provide the desired connector type, and unfortunately I don’t believe such a device exists.
Sorry for the bad news, but hopefully this helps shed some light on the situation.