I am using W7 which works nicely but I’d like to switch to Mac and use Cubase and the MR816X that I own and love. 
Please tell me that they work like a charm together.
If W7 is working nicely for you, then why make the switch? Considering the fact that the new iMacs have no FW ports and you will have to connect into a Thunderbolt adapter, would be a non-starter for me. Too much risk IMHO.