Thanks for the review, like the other poster I look forward to the Taichi Z390 Ultimate review, as that is the board I'm inclined towards from a feature set perspective, and perhaps it will show improvement with newer firmware.
At of today, it looks like ASRock has made a 1.38 version BIOS available as a "Beta" release. I"m going to sit tight and track their BIOS releases before building with the i9-9900K. I'm a little surprised there hasn't already been more evolution as the vendor has had these boards and CPU's to test with for quite some time now.
The Tachi Z390/i9-9900K power draw, combined with a single newer RTX 2080 GPU, isn't going to leave allot of head room for a 650W power supply.
A couple other more minor details for ASRock (and all mobo manufacturers) to consider:
(1) Please make the integrated USB type A connectors color coded to reflect their version. They're all blue, which means you look back there to plug something in and then have to grab the manual or pull up a PDF to see which is 3.1, 3.0, and so forth. That's the last thing you want to do.
(2) Also, a couple "dummy" SATA plugs which the consumer could plug into SATA headers which are disabled when using M.2 drives might save people allot of grief, and possibly even prevent some support calls.
(3) Thank You ASRock for including DTS Connect! Allot of us have nice high end surround speakers you can't or wouldn't want to drive directly from the mobo, and connecting a monitor at greater than 60Hz (or via DisplayPort) makes HDMI audio pass-through to a home theater receiver a non-starter. DTS connect (or Dobly Digital Live) should be a standard feature from every mobo vendors mid-tier or better products.