Got ASRock H97m-itx working with the help of webstar
here.
I had to do TWO THINGS
1)put the 3 kexts into the EFI/Clover/10.12 (the two discussed here and USBInjectAll.kext)
AND
2)actually type in these entries in the kext section of clover configurator(to increase the port limit)
Name = AppleUSBXHCIPCI
Find* [HEX] = 83BD74FFFFFF10
Replace * [HEX] = 83BD74FFFFFF1B
So I got USB 3 working!
But I read Rehabman's post
here, and he goes to great lengths to say that
USBInjectAll.kext is a temporary fix
'This kext attempts to inject all ports for each controller, and for hubs as well.'
Although the
video by Ibrahim that webstar linked indicates that the patch increases the number of ports to 26, Rehabman says you only need 20 (except for 100 series - H170 and Z170).
Rehabman also says
'The config_patches.plist also contains the DSDT patches required to rename EHC1->EH01 and EHC2->EH02 which is important to avoid collisions between this kext and any built-in port injectors in the native kexts for your SMBIOS.
Note: Do not plan to use the patch long-term. It could be problematic. If you have more than 15 ports on XHC, you should use FakePCIID_XHCIMux to route the USB2 component of those USB3 ports to EHCI. It is easy to stay under the limit if up to 8-USB2 ports are routed off XHC.'
But I have no real understanding of what that means. Or where to begin to understand that paragraph.
An even more complicated exposition for El Capitan is
here and
here. In that guide, he looks into a file named
/System/Library/Extensions/IOUSBHostFamily.kext/Contents/PlugIns/AppleUSBXHCIPCI.kext/Contents/Info.plist
But I have NO IOUSBHostFamily.kext in my extensions folder - so maybe Sierra changed things again after El Capitan.