Hi wessltov,
Welcome to Microsoft Community and appreciate your time taken for sharing detailed information. I understand that Outlook notification sounds do not use selected audio device. I am glad to offer you help on this issue.
You could change your headphones to the output device in Device Manager, which is fine, but Outlook as an application generally defaults to the first monitor as the output device. You need to set your headset as the output device in the application Default device. Here are the steps:
Click Start > Settings > System > Sound > Advanced sound options > Outlook > select the output device you want.
This way makes Outlook sounds play over a different hardware device than all other sounds.
Hope this works. If any update, welcome to share with us.
Best Regard,
Kevin | Microsoft Community Support Specialist
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