I'm buying some good headphones and I want to know how to improve the audio signal coming from my Mac Pro. Would a digital audio interface be the way to go? If so, which ones would be good just for a listening setup. I won't be recording. I have a vintage Pioneer amp that I'm currently using too, so that could be used in the setup or not. I'm also wondering about mobile listening. I have a 5th Gen iPod classic and an iPhone 4. Is there a setup people use to improve sound there? I've seen a few options using a small amp connected to the dock. Maybe there's one option that could be used for both? Some sort of portable amp that would accept either a USB/Firewire or dock connector? I don't know, just guessing here. Any feedback is appreciated.