I used the HD485 for years before I found this site. When I got my X-fi Elite Pro, I noticed that there was a big improvement. I wondered what else I was missing out on, which eventually led me to head-fi.
A few days ago my USB dac, The Bloat, arrived. On my HD485 it was a noticeable improvement, but really not that different from my x-fi. If anything, it was probably the amplification that improved it.
Finally, today my HD580 arrived. Now, it is used so I expect that it has been "burned in". I plug it in and listen to Neil Young's Live at Massey Hall. There is a noticeable improvement, but really the biggest difference is small details. In fact, I would say the HD485 on my x-fi has 90% of the sound of this $350 setup. I listen to Money by Pink Floyd...there really isn't a huge difference at all.