The easiest answer to your requirements without breaking the bank is the HD 600. I have never listened to the FiiOs of the world and don't intend to either. Neither will I invest in a DAP. However I highly recommend the Geek Out as a portable DAC/amp. From a desktop DAC/Amp perspective, get the Modi 2 Uber as a DAC and the Vali or the Asgard 2 as amp. If you are going with the Senn HP, get the Vali. Else get the Asgard 2.
As an alternative to the Senn HD 600, I like the AKG7xx. A bit warm but nice midrange and sweet treble. Very easy to drive. I've plugged it into my iPhone, laptop with and without DAC/amp.