iMac 5 (Retina 5k, 27-inch, Late 2014) can be downgrade if it comes with Yosemite pre-installed from fabric?

Please somebody!!! Has anyone downgrade a iMac 5 (Retina 5k, 27-inch, Late 2014) pre-installed Yosemite from fabric to an older version of Mac OS??

My Pro Tools 10 does´t work with Yosemite. I have two days to resolve this, if not I have to return the computer.

If somebody has done the downgrade please give a step by step solution! I have tried it to downgrade and it appears this symbol: HELP HELP HELP!!

Thanks