ok thanks for the reply 
i installed sierra to this mother board i just had a problem with uefi booting from hard disk.
motherboard boots from usb but not from hard drive, so i found the solution by adding uefi boot information to bios with this link:
tony's site /threads/guide-asrock-uefi-boot-fix.174726/
i did not used any special thing, i just used unibeast for creating bootable usb..
there is no flag on boot, no external file added.. just unibeast for sierra.
then system opened with hd4600 recognised with 1536 mb ram
i used multibeast for post install.. just selected usb3 fix , ethernet as atheros, audio alc892 thats all.. it runs now flawless..
by the way i am building a metal mac pro 2013+ case hand made with metal spinning method..
you can follow it from
tony's site /threads/mac-pro-mod-with-custom-shaped-thin-metal-sheet.207083/
