I admit I forgot the replaceable amps which are great...the UI, let s wait and see. The 901 will not allow the Dac function unless you get the dock and the battery life is still shorter, from what I am told. Design is just a matter of taste. Both great players indeed, I feel one is a better all rounder if you want portability while the other has better SQ and can scale more with the amp cards.
I find the replaceable battery of the HM-901 a huge selling point to me. How many electronic devices in the long haul - whether it be phones, ipods etc. where the usual reason/gripe for parting with it is the battery? Quite often in my case. That's huge to me.