Audio jack is another one. I have some nice open-back headphones and they don't have USB. I think it's actually fairly unreasonable to expect the entire audioph

Audio jack is another one. I have some nice open-back headphones and they don't have USB. I think it's actually fairly unreasonable to expect the entire audiophile headphone market to convert to digital; it makes more sense to do the DA conversion on the phone/computer, especially since some audio sources are analog anyway.