Ahh, I loved my old MX300....
What would you consider a "basic" sound card?
Well, I was going to recommend a TB Santa Cruz card, but it's certainly more than "basic". Take a look at the Hot Deals forums, as I saw a post about a TBSC for $10 after pricematch and rebate. Excellent sound, 6 speaker support with VERSAjack, etc.
As far as basic sound cards are concerned, you probably couldn't go wrong with some of Creative's lower end cards (if all you need is 2 speaker and gameport support).