Apple has a new default sound effect for volume up/down now. "Flatter" to go with the new visual language. Sounds like the same tone for both volume up and down, which seems like a step backwards to me.
Kalila: sorry, no other ideas for troubleshooting.
i just notice that installing 892 kext with MultiBeast 6.0.1, then patching kext with MultiBeast 6.4.x for 9 series compatibilities and MultiBeast 7.x.x for 3 ports audio works for my Asus Z97I-PLUS.