I thought this was interesting.
http://apnews.excite.com/article/20050121/D87OFTBG0.html

I know this wasn't the point of the article, but...

In reply to:

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There's simply no better way to enjoy a well-mastered recording than with well-designed headphones with a wide frequency response range to provide a fuller sound quality to the music.

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I presume that means he doesn't use AAC or MP3 encoding for his audio (or that at least, he encodes at 320 kbps). A 128 kbps mp3 certainly doesn't have a wide frequency response range, and the AAC, while better, isn't all that and a bag of chips, either. I'm happy to encode at 192 kbps for my iPod because I'm not looking for insane performance in portable music. I just want to have something to distract me from how long I've been on the treadmill or for commuting on the subway.

Can't wait for someone to make something like this for the iPod shuffle. I'm getting one, but I'm a little concerned about it working well with my Senn HD570s. Of course, if it doesn't, no great loss... I can always use the PX250s.

$150 ain't bad for a headphone amp.