Yes, at the moment it only works with the Built-in Audio Device. The reason is that I'd like to use the private DSP API inside Apple's HDA Driver in the future, which would further reduce CPU usage to approx 0.5%
it seems to work great :D At the same time, this doesn't seem to work with Hackintosh Mac, since they may use different driver, headphone not detected.
But it works great with my macbook :D