Ah OK, well I'll try it with more ports :)
Yep everything up to date, but the SMBIOS is named iMacPro19,1 - so just generate a new one as a MacPro7,1 then it'll work?
Is it true that you have to plug in 1 USB 2.0 then 3.0 device in each port, 1 at a time after each 5 second pass? As some guides...