Hi, @Chris
Thank you for posting in Microsoft Q&A forum.
Look like the PXE issue is related to your MP issue, we have to fix the MP issue first.
The HTTP status code 401 could caused by many reason, you may check MPControl.log and IIS log for more details.
Make sure the default IIS port (80) was not used to some other website.
https://social.technet.microsoft.com/Forums/en-US/15073010-6665-4e68-8d5f-9c706750c43a/http-test-request-failed-status-code-is-401-unauthorized?forum=configmanagergeneral
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