For "computer" speakers they are rated as being very good. that is where the rated as good ends! One problem is that they offer no future upgrade options and for the same or less cost (decent quality used) you can put together a system that will sound a whole lot better and offers the ability to upgrade the different componants a little at a time for even higher performance and in case of a componant failure you are not tied to one brand or model of equipment to get your system back to full health.
If you are serious about wanting the best then you need to quit looking at computer speakers and start looking at home audio equipment. Craigslist is your friend here, many receivers a few years old are available at very cheap and reasonable prices that lack some of the newest home theater features but will be ideal for your use.
Same with speakers, just because a speaker is a few years old if it has been well cared for and not damaged or abused they can be bought for a fraction of their new price, again allowing you to put together a nice system for a reasonable cash outlay that can be upgraded to be even better in the future if you feel its warranted.
Your existing soundcard will work fine to send the signals to the receiver, just make sure that the receiver you buy has the correct inputs on the rear to accept the type signal you want to send from your soundcard.
The only disadvantage to moving to the home audio type of equipment is it can be a sickness like building and upgrading computers, to start with "this is fine and great" and then the sickness progresses to where you are finding yourself changing and using pre-amps and seperate amps, buying better and better speakers, more and bigger subs, depending on how bad you get the sickness depends on how much damage you do to your wallet.
Do yourself a favour and forget the "computer" speakers and then you are on the road to truly "enjoy the sound the way it was meant to be heard." Not to mention its another fun (but can be expensive if you are not careful) and interesting hobby to get involved with and to learn about and enjoy!