Yeah I did use the Steinberg tool. I put in the DVD disc containing Cubase Artist 7 and choose language. Then I swapped to the installation tool for Yosemite and went about the installation. It went fine. It even prompted me to put in the Sonic SE disc. To do so I had to close the installation window for Artist 7 in order to get the disc out and put the Sonic SE disc in. Things then continued to install. Then download manager (name?) initiated and downloaded the latest patch. After this the installation was done and successful according to the installer. But I can’t find Cubase on the damn computer 
I’m just now downloading the complete Artist 7 installer from Steinberg’s website to try to install from it instead from disc (with help from the Yosemite installer tool).