An external USB dac will give the best sound. You can get one with just an amplified headphone output for cheaper or one a bit more with auxilary outputs to hook to a home theatre/speakers or even analogue inputs to hook up a cell phone, etc...
Now using an external DAC will give the best DAC quality for your dollar compared to any soundcard on the market. But you loose all the fancy software it comes with. No big deal. Use the EQ of your music player software be it media player, winamp, foobar, itunes, etc... And for virtual surround sound with headphones use Razer Surround. That's better than dolby headphone and Creative's alternative.
If you want to order a DAC check out Emotiva. They have the little and big ego. But they are a bit over budget at $150-$200. Check out local music/guitar instrument stores. Go to the PA section and they should have some USB dacs there. I like the M-Audio Super DAC which is right around the $150 mark. You can plug in your speakers and headphones and just switch betweeen the 2. There are cheaper dacs under $75 which are fine as well. There is tons of selection...way more than with soundcards.
You will not get better sound quality than a USB DAC. Case closed. And the DAC can be transported to future computers, cell phones, tablets, or laptops easily. All a soundcard is, is a cheap dac with some software. An actual DAC is a good DAC with no software. You don't need the software.