Oh boy... where do we start... I have to start assuming here, because you didn't include much info, but "ASSUMING" that you are using the balanced (2) outputs (balanced means TRS connectors, you can use TS type, but the signal will not be the same as with TRS on both ends) (2) outputs on the back? I would assume that there must be some internal, software driven menu item that allows you to adjust the output volume of the Apogee with respect to different devices and applications...Then we need to discuss where you are plugging into the HP 60?... Again, assumption = input A/B...???all these things are going to have an affect on the volume @ headphones, but my money is on the output volume of the Apogee... which is an Apogee issue, not a Presonus one.