This has nothing to do with the computer and/or the S4. These are "Traktor" and/or sync problems. These are valid points and need to be addressed, but have nothing to do with the funktion of the S4 and the computer (mac 10.6.8). It either works, or it doesn't. After that, you look at other things. I think you have something interfering with signal via usb. I know the aftermath of soundflower and jack on my mac made me rethink the possibilties for error. Best of luck.