Soundcard: For audio the EMU 1212M and 0404M are all the rage, they are roughly $200 and $100 respectively and can be had at Guitar Center among other places. They are internal, but reportedly very low (electical) noise. Almost nothing else gets recommended for under $500 soundcards since these came out.
As for external DAC, thats what I use. What do you consider rediculously expensive? The Benchmark Media Systems DAC1 is $975, was the 2004 Stereophile Editors Choice and has an excellent built in headphone amplifier.
For headphones, I'm not a Grado fan but given what you listen to I understand why you are. You might also look into the allesandro MS1 (http://www.alessandro-products.com/headphones.html
) the allesandro line are tweaked grados, they are a little less bright but have the same up front, fast sound. The MS1 is a tweaked SR125 and sells for close to the price of the SR80 so, it is a good value thing.
Oh yeah check out www.headfi.org
for headphones and also soundcard stuff in the computer as source forum. There is supposed to be a meet in Portland in March, I should be there with the DAC1 and some Sennheiser headphones, I'm sure there will be grados and probably a couple of computer setups.
DVD-Audio, you won't get full rez on NIN or anything else copy protected in general. I remember reading once that some soundblaster cards would output full rez dvd-audio as pcm via the digital out, which you could record via digital in on a second card. You can't just play it on said soundblaster card because all soundblaster cards resample analog to 48khz, including up from 44.1 where applicable. There is the toshiba 4900, and pioneer 563a. Both are $150, play dvd-a, and have gotten a lot of attention on audio asylum and the like, I had the pioneer for a while, its worth the money just as a dvd-v player, it plays sacd too, no complaints on the sound at the price.