In the past there was an issue with USB disconnecting and reconnecting but that was solved by AMD and Motherboard Manufacturers with BIOS updates. This issue affect only the 400 & 500 series Motherboards.
I don't see how the processor would affect the Motherboard's Audio since it doesn't have an Integrated Graphics on it.
The motherboard has its own Audio graphics drivers. The only way possible that the Motherboard Audio would not work is if the User has a GPU card installed and is connected to a Audio Device which is made the Default Audio Device which would then use the GPU Driver's HD AUDIO driver and not the Motherboard's driver.
In Window's Sound Panel if the Audio Device that is connected to the GPU is the Main Default Audio Device that will automatically disable the Motherboard's audio.
As an example only here is my Window's Sound Panel with my Bluetooth Headset as the Default Audio Device:
Since your friend says his Motherboard Audio works with other CPUs but not with the 5700X I also find surprising.
The AMD 5700X has, as far as I am aware of, nothing to do with the Motherboard's or GPU Audio drivers.
