It appears to not be a fundamental limitation of the 2080 ti. https://nvidia.custhelp.com/app/answers/detail/a_id/2796/~/which-hdmi-audio-formats-do-nvidia-gpus-support%3F
(I have a 2080 Super, but I only use a DP connection to a monitor that has no audio.)
What digital audio device shows in the nVidia control panel?
Is stereo the only speaker configuration available in the Windows Sound control panel? (I suppose that you're running MS Windows 10.)
If none of that works for you, there are switches to take multiple optical inputs into one output. Search Amazon for "optical audio switch".
(I have a 2080 Super, but I only use a DP connection to a monitor that has no audio.)
What digital audio device shows in the nVidia control panel?
Is stereo the only speaker configuration available in the Windows Sound control panel? (I suppose that you're running MS Windows 10.)
If none of that works for you, there are switches to take multiple optical inputs into one output. Search Amazon for "optical audio switch".