virtualbox.org

Host system Windows 8.1
Guest system Windows 98SE
Only purpose is to hook up Sound Blaster
Creative Sound Blaster Extigy 24-Bit External Sound Card EAX Advanced HD SB0130

Which is an external USB sound card with great specs.
Is this possible? The guest seems to already have the "Sound Blaster16"
Thingy. It will not see the external and so will not instal driver.

Does this have any chance of working?

The guest seems to work fine.

When it's connected, the Extigy replaces your sound card. But to prevent configuration issues, your system reverts seamlessly back to your internal sound card when the Extigy is disconnected or powered down. - under Windows98 that is!

I installed the extension pack to no avail. I cannot get the host to give up the USB port that the external sound card is on.

Did you configure a USB filter for the sound card in the VM configuration?