I love my HE400, but starting to get the itch for something new.   What would be some options for a worthwhile upgrade that still has that fun sound signature like the HE400?

Hoping for some help to find the ideal "transportable" amp/dac for the HE400 in the $250 - $500 range. I've been running an E17 but I'm looking to make a final upgrade and bring out the HE400s full potential. I connect to an old Macbook Pro, iPad/iPhone, and a PC with a poor sound card.  ...

I'm new here so I really have no place to be making suggestions, however, I do frequent A LOT of forums. I've been browsing the classifieds sections a fair amount and something that is very frustrating is that prices are hardly ever kept intact.   Many forums require that prices be left up...