This new MacMini that I bought came with preinstalled Yosemite already.
I tried booting it with a bootable USBs that have OS X 10.8 and 10.9 on it, but it wouldn’t boot.
I tried to partition the HD, which is FusionDrive by the way, so I could install the older OS X version on it, and still it wouldn’t let me run the installation for OS X 10.8 and 10.9.
Then, when I run the Startup Manager, I used Disk Utility to erase the HD and tried to recover it from the bootable USB.
After that the Mac wouldn’t boot at all! - what happened is that I erased everything on HD and couldn’t run the Mac on an older OS X version that was installed in that way and couldn’t use the computer - the grey screen with circle and a line would appear after which it turns itself off.
I disassembled entire Mac (good buy warranty), took out the HD and connected it to MacBook Pro via Thunderbolt-FireWire cable to try to install OS X 10.9 that way. After installation, I put the HD back, but the Mac wouldn’t boot.
I restarted it, connected the Time Machine HD to which I made a backup before I tried any of these approaches, and restored it to it’s previous state.
So, now I can boot it, with a Yosemite running on it… but still can’t use Cubase 5, nor upgrade to 7.5!
In the end, I read somewhere that the problem are actually drivers for the components used on the MacMini late 2014 which exist only on OS X Yosemite and not the older OS X versions.
I turned to Apple and asked for assistance - I was said that it should be expected from Steinberg to come up with a solution in a couple of months - meaning
they should develop some kind of another installation tool or an update or something 3rd…
I sent e-mail to Steinberg yesterday, asking the same thing, but they haven’t replied yet.
I found that other users experience the same problem with Cubase 5 and Yosemite…