Well, that's unfortunate. I've recently been playing The Elder Scrolls III: Morrowind for PC, and was reminded just how much I love having surround sound. With 2.1 speakers, you only get the illusion of having surround sound, and that's only with clever sound positioning (for I can't think of what it's actually called at the moment).
Oh, and make sure to get 2.1, as I know firsthand how a set of speakers from a good brand (Logitech) can sound without a sub. (Unless you can deal with little to no bass, and since you used the X-540s, that's unlikely.)