Well, I answered my own question. I cloned my HD first, just in case, then installed Yosemite and updated everything, included iTunes. The W4S DAC2 driver works fine. As a matter of fact, I didn't have to restart or reset anything. iTunes 12, the DAC-2, Audirvana 1.5, etc., all working as they should. Perhaps this will help anyone with similar gear.
10/22/14 at 6:20pm