Increase Virtualbox 6.1 AV Performance for Win10 Guest / Run Win10 App on Ubuntu 18.04

[yupthatguy]

I have an Acer Aspire 5 machine dual-booted with Win10 and Ubuntu 18.04

I installed a Win10 app in Ubuntu 18.04 via Virtualbox 6.1 with a Win10 guest that requires my mic and camera for an online course that I teach. I also installed the relevant Virtualbox Extension Pack and downloaded all of the Win10 updates. The VDI file is 100 GB, twice the recommended size, I give it 4 out of 8 CPU cores and 4096 MB Base memory (while also closing all other open applications/windows on the Ubuntu 18.04 hosts).

Result:

Video works perfectly. I just need to add it manually via the Vbox "Devices" after the starting the virtual machine. IF I try to enable it via VBox machine settings "USB Filter" prior to launching the machine, the webcam will not be recognized and I still have to manually start it after I boot VBox into Win10.
Audio simply will not work.

First, students couldn't hear me. Yes, I verified "Audio Input" was selected under Vbox "Devices" menu.

Secondly, when I emergency booted into Win10 to continue class, students oddly still could not hear me. I literally had to run out and purchase an external mic. It seems that Virtualbox 6.1 / & Extension Pack somehow negatively impacted my built-in microphone on my actually Win10 partition (bios?, driver issues? Don't know.)

Thirdly, now if I boot into Win10 and try to use my application without a mic, there is "feedback" noise only audible to students if I don't use my external mic. Even after re-boot problem persists. (Update: after several re-boots this issue seems to have vanished)

Can someone provide reliable settings to run my windows 10 application in Ubuntu with quality audio / video... ?

thx