Soundcard / Headphone questions...

I'm new to all of this, but I'm sort of getting a handle on what my needs are.

I'm looking for an improvement over my onboard sound chipset (which is a pretty generic Realtek sound solution). I'm on a custom built desktop and I'm into gaming. I'd also like a new pair of headphones that won't break the bank (I currently have Sennheiser HD555s but I'm a bit bored with them).

The games I do play tend to be RPG / strategy, rather than FPS where positional sound would be super important, though. I'm also pretty big into music, across a fair number of genres. At the moment, I'd say I listen to a lot of indie/alternative rock, some metal, and some electronica. I'm not a basshead, but I would like -some- bass.

I guess I feel I'm sort of 60% music / 40% gaming with my current set-up. I'd like a headphone / soundcard or DAC combo that would be ideal for that, which combined would be less than, say, $250.

For cards, I've got the impression that you ither go X-Fi or Xonar, though I wouldn't know what specific models to get; for headphones, I've heard that the Samson SR850s are a great bang for the buck budget headphones that some people claim outperform the HD555s, even, despite being less than half the price. For headphones, I guess I'm mostly looking for a full size open-back pair that would be well-rounded and good for most types of music. OK if it's light on the bass, just not too light.

Final question: if I had a sound card, would I need an amp? Or would the extra power from the soundcard serve as an amp, or what?

Thanks for any guidance!

X-Fi Titanium HD is out of my price range, unfortunately. Looking at Xonar cards, the D1 / DX seem to be in my range, though. I could also go to the DG, but I don't want to go -too- cheap. I assume there will be a noticeable difference fom the DG to the D1/DX? I don't know if this is true, but one of my friends told me that lower end sound cards runs the risk of being no better from on-board audio, which is what I fear might be the case with the DG? Actually, I have no idea, but I'm just wondering if that's a possibility.

Anyway, I'll probably go for the D1/DX.

Thanks