I can't wait for the day to come when headphones fit under helmets. I went to best buy lst year and bought 3 pairs of headphones thinking one would fit and none of them were even close. The easy part is making a thin band that goes under the helmet but where you'll run into a problem is the actual speaker/earmuff part because most helmets fit pretty snug around the ears. I have a gyro helmet with the gryo speakers and it's ok sound wise when you're not moving but once you start to ride the music gets washed out really badly. I tried the scull candy buds and theres no way i can keep those things in all day, after about 2 hrs my ears are in crazy pain because of pressure points. I went on a trip a couple weeks ago and left the helmet and used my headphones and i was in heaven.
sounds like your using the wrong size ear pad thingers. when you bought the skullcandys they should have come with 3 or 4 sets of different ear pads. (cant think of a better word, theyre the rubber things that go in your ear) if your using the right size they should be comfy indefinetly