Edited by MarcadoStalker7 - 6/17/14 at 8:21pm
the Schiit Magni and Modi work well with the HE-400 and it will work fine for the HD 598s as well.
you connect the Modi (DAC) through usb so it will work with you computer, or you could bet a LOD to usb for your ipod and connect it that way.
so, do you wanna connect ipod to modi DAC. well, it is not possible.
E18 can work as dac for specified models of smart phones. look here, http://www.head-fi.org/t/685414/preview-fiio-e18-kunlun-surprise-surprise