Installing Mavericks on a new Mac Mini (end 2014) shipped with Yosemite pre-installed?
The general rule is, you cannot instal an OS on a Mac that is older than the Mac itself.
See Don't install a version of Mac OS X earlier than what came with your Mac

That said, Cubase 7 should run OK on Yosemite, though you will need the Steinberg Installer patch. I don't know Studio One 2 so I can't say on that.
Google did find this from Presonus about it.

Edit: I also found this, officially qualifying Studio One 2.6.4 as Yosemite-compatible