I believe you are misunderstanding what the string in parentheses represents.
Audio In/Out is handled by a dedicated sound chip, in your (and my) case that is a sound chip on the motherboard.
The "MAC address" you mentioned is a typical PCI ID you'd see on any other PC.
Your sound chip has a PCI ID assigned to it.
The IDs you see here are comprised of a Vendor ID and a Device ID, separated by a colon.
A sound chip may have multiple audio inputs and outputs, but they all belong to the same sound chip, all inheriting the same PCI ID.
P.S.:
MAC addresses are a networking thing. They live in OSI/ISO layer 2, aka the Data Link Layer.
If you want to look into currently assigned PCI IDs, click here.
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Comment by @in-a-dil-emma