a new public beta is out for Mac. The new version supports 10.10 Yosemite and also features new audio and MIDI drivers. 48k sessions should run smoother now and we also fixed a couple of sleep mode related issues. The release is Mac only at the moment but there will also be a new Windows version in a couple of weeks.
A hint for you: due to some changes Apple has made in the last OSX updates, it might be necessary to un-install the old version first using the un-installer in /Applications/Access Music/Virus TI/
5.1.0.can be found here: http://www.virus.info/downloads