Best computer speakers ~300$ budget

if you want to truly get the best sound you're going to want to look at hifi/home theater speakers and not pc speakers.

with that said, if you're wanting surround sound unfortunately a soundcard really isnt going to be as helpful as you will want a receiver to handle the speakers and hdmi is the best way to connect that. for $500 you could go with the energy 5.1 classic (or the monoprice 10565 clone of it) paired with a receiver. for that sort of price its going to offer one of the better buys in terms of audio. there are other sets which are good, but the energy set is well known and trusted. of course you could use optical out of the soundcard, but optical < hdmi in terms of quality.

if you really wanted to use the soundcard yet did not want pc speakers - you could always go with some self-powered bookshelf speakers. those would plug right in to your soundcard. they would only be stereo, but would certainly offer better audio than pc speakers. likewise, if you went with only a 2.0 or 2.1 setup you could use a stereo receiver and two passive speakers and have that hooked up to your soundcard via 3.5mm or optical. depending on your taste in sound, there are many options to choose from. i myself like the very bright lively treble found on klipsch speakers (horn style tweeters are brighter than dome style tweeters). you might like a pair of klipsch bookshelves if you are like me, otherwise there are other good choices to go with depending on exactly how much you wanted to spend. for a lower budget, perhaps the pioneer bs22 with a budget amp. for a higher budget perhaps the klipsch icon with a stereo receiver. for powered perhaps the audioengine a2 (but they are heavily influenced by positioning).