Update: got myself ASUS ROG Zenith II Extreme and all issues that I encountered on Strix are still present on Zenith, that includes:
Audio issue on optical output:
- audio crackling on Windows (with MS and ASUS drivers, doesn't make a difference)
- audio stops working after some time, reboot and starting playback again resolves noise that comes after that event
- SATA performance is lower then on x299 for small reads, burst is same
- inability to disable individual SATA drive in BIOS
In all cases tested with latest BIOS - 0702.