If you don't have high impedance headphones (50ohms+), this will trigger the 32 bit Hi-Fi DAC in AUX mode...
Use an adapter before plugging in the headphones...like this one
http://www.amazon.com/gp/product/B00KE5NJ7W/ref=s9_simh_gw_g107_i1_r?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=desktop-1&pf_rd_r=00QG93QGGDGC1PAAH602&pf_rd_t=36701&pf_rd_p=2079475242&pf_rd_i=desktop
I use the extended headphone adapter that comes with LifeProof smartphone case, which works well for my SONY MDR-XB90EX IEMs.
If you have headphones that have a detachable cable, plug the cable in first without the headphones and then connect the headphone...this will also trigger AUX mode.