I've got a 27" iMac with a Focusrite Saffire 6 USB external soundcard, with a pair of KRK VXT6 monitors. When alternating between playing music through iTunes, Soundcloud, YouTube & Ableton, at some point in time the music will just stop completely. All power is still running through all the devices. To fix this I have two options. Sometimes I can simply un-select and re-select the external soundcard as my default sound output and that will work, but very rarely. Most times I have to turn the monitors off and restart the Mac. Extremely painful and annoying. I've tried re installing the software, there's no current updates that I don't have. If anyone can help me out here please let me know! I'm trying to find out whether its the Mac or the soundcard that needs looking at.. Thanks in advance!