@lnxd Got it working. Not sure if it was the vBIOS or the GPU audio but I've now survived several reboots and shutdowns with no Error 43 issues.
Per your suggestion, I loaded GPU as 2nd graphics card (I also enabled the GPU audio to be safe) and dumped the rom with GPU-z.
Removed VNC from VM used the rom I just dumped.
VM booted right up with no issues.
Attached second monitor for testing, rebooted, shutdown, still no issues.
Thank you for your help on this.
EDIT: For anyone wondering, I've loaded two VMs, one with Non-WHQL 2020-21.3.2 drivers and one with 2020-21.3.1 drivers. Both work fine and I'm able to shutdown/switch between both without issue.