A little back-story first I suppose.
The computer in my sig is what I use currently. I have an ASUS Xonard D1 in there somewhere. I have been running that to Klipsch 2.1's for the last five odd years or whatever. I'll be building a new computer this year, albeit kind of an ongoing process - just picking things up when I see good sales and such, but I plan on changing a few things in my next build.
1. It will likely be an mATX board with no PCI slots (D1 I have is PCI)
2. I already have some new speakers/headphones and would like to at least attempt to feed them well.
My equipment and sources: ATH-M50, Senn 485, Audioengine A5+, probably half FLAC, half MP3 320
So my question(s) really come down to this. What should I get, an internal PCI-e soundcard with a headphone amp, or get an external AMP/DAC that I can use for other things too? It'd be nice to take the DAC around the city/train/bus if I wanted to, but definitely not a requirement. Don't have too many requirements, really. I'd rather not spend a whole ton either (100-200USD?). I'm willing to consider either option at this point as well.
I was hoping for specific suggestions too, rather than general ideas. All are welcome! Even if it's not some set up I have listed.