I've been using the HD 448 almost exclusively as my "portable" headphone lately, unamped from my ipod. I love the sound of it, and it is very light and comfortable, with a nice short cord, so it can easily be used for that purpose. It's a weird headphone, because it almost perfectly straddles the line between portable and home use. I am unaware of any other headphone like that.
EDIT: On a whim I took another listen to the PX200-II's on my iPod playing Keyshia Cole's "A Different Me" album, which is surprisingly well recorded, produced and mastered with a phenomenal soundstage. While the PX200-II didn't image as well as the HD448's or the HD595's, it did surprisingly well, managing to present decent width and depth. Also, I finally found a sweet spot on my ears that provides me with more detail than I was hearing before, and while they aren't hyper-detailed in the mids and highs like the HD448, they are still detailed enough to sound good and are very smooth at the same time. In other words: Priest, I think you'll like them.