You will obviously get much better clarity from a top end soundcard than a garbage one, but I honestly don't think an average card will be destroyed by the best card out on the net.
To be honest with you though, if you're getting some kick ass speakers, I'd spend the extra bucks and make it worth your while by getting a good card. There doesn't seem to be much sense in capping your speakers over a sound card. Perhaps it would be better to talk with someone more informed on the effect of sound cards and speaker combination on clarity.