I'm not sure if this is an issue with how Crossover works, or with my particular Linux audio drivers. But one thing I've noticed under Ubuntu 14, while VDJ is running, since it constantly uses the audio card, no other application can use the sound. So for example, while DJing, I pull up a YouTube video for a song I can't find in my library, it won't play unless I close VDJ first...
I'm pretty sure Ubuntu uses the ALSA drivers, which should support multiple applications using the audio output... so is this a Crossover issue or just a fundamental driver issue? It's always nice when DJing to be able to have a video cue'd up in YouTube and go back and forth between the browser and Virtual DJ Studio. In Windows this is a non-issue. I only noticed this last weekend, while trying to play a Karaoke tune in YouTube - had to close down VDJ before it would allow the browser to play the audio...