Interestingly, many people have been using digital out into a portable high quality dac/amp on a range of devices for many years. Quality blows away anything in

Interestingly, many people have been using digital out into a portable high quality dac/amp on a range of devices for many years. Quality blows away anything inside a phone or headphones, and can drive larger headphones, and has an analogue volume control, multi jack outputs and separate battery supply. I would recommend this option over old school headphone jacks or new "digital" headphones.