I have the Gigabyte board and a UAD Apollo Duo with the TB adapter. They work great together, even though not officially supported by UA. Only thing I've found is that, even though UA says to make sure the Apollo is on before booting the computer, with Win8 Pro 64 bit it is sketchy whether TB devices will be seen. If I turn on my Apollo after the computer finishes booting, it runs flawlessly!
Can't comment on Cubase 5 - that's old software! I'm running C7.05
BTW, this mobo is a great platform for a Hackintosh also.