Irix "uses?"

I'm sure there are one or two SGI boxes still ticking out there, but I haven't booted mine in months.

No, but it is used for "serious audio" as in professional music and other media production and is Unix as in Apple went and paid Open Group to certify it as one. I thought this was fairly common knowledge and you'd be trying to refute one or other. But yes, a specific Unix system (macOS) is used for stuff that most people would consider serious audio, and OSS is not involved unless it's hidden somewhere under layers of Core Audio.