OK. FYI, the M2Tech uninstaller script was run but didn't seem to do the job. Putting in the commands manually into Terminal resulted in a full uninstall, paving the way for the new Yosemite-compatible Young driver.
I can confirm that a Yosemite Mac can run PureMusic 2.0.2 and drive the M2Tech Young DAC perfectly capably. No critical listening done but no signs of any untoward activity.