Audio issue when HDMI drawing tablet is connected?
1. Facebook Huion Thread

I found a thread with your issue on the Huion facebook page. They suggested there trying to re-install the drivers for this particular device there. The thread.

This was the verbatim from the support person in the thread:


  Huion Cerine Oshiro
  
  Please try to reinstall the driver from our website to see if it
  helps: https://www.huiontablet.com/support/ Here's a step by step to
  reinstall, please try and see if it works:
  
  (If you are using Mac system, please skip 3-4 steps）
  
  
  Log out the Huion driver, close all drawing programs you are running, close your anti virus software.
  Uninstall the Huion driver from control panel.
  Find the TabletDriver folder from C:\Program files\ and delete it. (If you are not able to find this folder, that means you have
  deleted it already, and you may skip this step.)
  Go to C:\windows\system32 or C:\windows\system64, find wintab32.dll and delete it.
  Unplug the USB cable.
  Download driver from Huion website and install it as an Administrator.
  Reboot the computer and wait until it finishes rebooting.
  Plug the tablet back in. If the problem still persists, please send your problem to:service@huiontablet.com to get instant technical
  support, thank you!
  


2. DeviantArt Thread

I also found another thread mentioning a prior version of a Huion device, Huion GT-185 HD. This is a tablet monitor which I assume is the same type of item as your Huion Gt-220.  The thread was on DeviantArt page for the GT-185 HD device.

In the thread a Huion support staff made the point that these tablet monitors do not include audio.


  huion Oct 20, 2017 
  Hello,
  
  Kindly note that there is no audio device in the monitor, so it can
  not give off any audio.


They then went on to suggest that the ordering of the displays mattered because of this fact.


  huion Oct 23, 2017  Hello,
  
  Yes, it supports extended mode. Kindly inform you that if you want to
  use the monitor in extend mode and then use the pen on the HUION
  monitor, you need to go to control panel to identify Huion monitor is
  recognized by which monitor in your system. For instance, if GT-185HD
  is monitor 2 in your system, please select Monitor 2 in the driver. If
  you have selected Monitor 2, but you still couldn't use the pen on it,
  please try to select "all desktop area".