I just installed Cubase 8 and Groove Agent 4 on a brand new, updated Mac Pro running OSX 10.11.4. Cubase starts fine and can use any VST instrument. Adding the GA as VST instrument in Cubase gives me the spinning rainbow ball of death, same for starting GA Stand Alone.
I have tried upgrading to the latest (4.2.3), Uninstalled and reinstalled, Re-downloaded and reinstalled, Uninstalled and deleted all associated files from various directories under /Library and .bom and .plist files, rebooting and reinstalling. It always hangs.
For the Stand Alone it hangs after I choose the audio interface (Initializing Groove Agent Version 4.2.30). The VST hangs after I try to add Instrument.
Anything else I should try? My next move is going to have to be to reinstall OSX.