This wasn't quite what I was expecting lol; maybe I need to clarify a little bit..
Why do you say that he won't appreciate the quality of the HD600? On re-reading my original post, I think I made it seem like he listens to music while moving around the house / office a lot, and therefore the HD600 + whatever amp needed to drive it would be an unideal fit for him.
I guess what I meant to say was that my doesn't really settle in one place to do anything that he does. I guess most people have their one place that they go to for everything, like their desk to do any kind of work, their listening station to listen to music.. but when my dad settles down to listen to music or to do a sermon preparation, it's always in a different spot: sometimes it's on the floor of his study, sometimes it's sitting on a couch, sometimes it's at his desk.. he doesn't really have a set go-to area. But once he's settled in, he stays where he chooses for hours on end. I guess this is why I wanted a more portable option for a headphone amp rather than one that required a dedicated power source.
But my dad is the type of person that actively listens to music. I find that when he decides to listen to music, all other activity ceases. I don't ever recall a time seeing my dad listen to music while doing something else. He'll pick his spot, put on his airline headphones (I swear, my dad's been using those free headphones that the airlines give out on flights for years now), and then he'll close his eyes and just enjoy the music.
I think music really moves him.. I also don't think my dad's bought anything for himself for years now (except for CDs). This is why I want to amplify (sorry for the stupid pun) his experience with something that I think will really allow him to enjoy the music. In that sense, I don't think the HD600 will be a waste of my money.
But I've never used the cans before, so I guess I wouldn't know. I know that if I get this, or the HD598 or some ridiculous headphone in the $1000+ range, he'll make it last forever.
Thanks again for the input.