How can I use headphone with my waist packs?

Well, for our E1642 & E1643, you can use the headphones through the zipper, and leave the zipper open a bit enough to let the headphones go out. (No need to worry about your zipper will open during the workout, the zipper lock from inside and can only be opened when you pull it.). There is another option too, add an earphone hole on the waist bag, it is not cost much, only USD0.1 more.