The common audio chips have lots of input/output pins (for complex surround systems), most of the pins are disabled but you can see them on stuff like hdajackretask. I can see that in my case they are on two separate outputs.
On a sidenote, on some systems the manufacturer doesn’t enable some unused pins on the OS side, but leaves them enabled on firmware, which can cause problems. So you can use this kind of software to disable them yourself.