I've got the volume slider in iTunes all the way up. I'm not even sure why that is even there in the OS X version. Then I have the computer output volume on the higher end, but typically not max, and the speakers somewhere in the middle of their range. I assume you get better sound quality with the stronger signal coming from the computer, but I'm nowhere near an expert. I generally just fiddle around with it until I get a good balance, as the volume of each device contributes to the overall EQ.