I would suggest the Soundblaster Live 24 Bit from Creative Labs. It's fairly priced at around 35 bucks ( I found 1 at my local Best Buy for 28 bucks ) and sounds great, comes with alot of nice tools also.
Don't let the 7:1. , 6:1 and 5:1 logo fool you, this card has full support from headphones on up to 7:1. I too have a 2:1 speaker setup and this card sounds fantastic with my speakers. You may be able to find it cheaper elsewhere, look around.