When I did a similar search for 9, everything I found (which was quite a lot) was a misinterpretation of a part of a 20 bit Sony signal for a DVD as if it were a 12 bit signal for device number 9.

I haven't had time to do a careful examination of the problem to see whether that is a flaw just in my decode system or whether there is a fundamental reason why it is easy to imagine a device 9 signal when seeing a 20-bit DVD signal (in which case Sony may have intentionally skipped 9 for that reason and you might also want to skip it).