Hi, I am looking to get a pair of open back headphones for Christmas. Looking specifically at the Sennheiser 58x Jubilee and Hifiman 4xx on Massdrop? I will mostly be listening through my Schiit Magni 3, but I would like to be able to stream music from my iphone. I know I'll need a portable headphone amp to drive the headphones. Can anyone recommend a suitable one? It would be great if it could also act as a dac from the iphone, but the ability to drive the headphones properly is the main thing.