I have not tried Dirac on Yosemite OS for at least a month, but prior to that I had all sorts of issues with Dirac (standalone, not involving Roon) on Yosemite OS, bad noise distortion. Unless their position has changed recently, Dirac did not officially sanction their software on Yosemite. They directedd me to some patches to see if that would improve the situation. They said Yosemite OS was the culprit.
On my MacMini I use Maverick v10.9.5 and have no issues with Dirac or Roon separately or in combination.