The funny thing is, the greatest relative utility probably comes from combining the expensive X-Fi with el cheapo speakers. Because the X-Fi's "advantage" over the Audigy 2/4 line is basically the new compression algorithm that increases volume on the transients (highs).
This works great for Logitech speakers that have no tweeters (since they hit a brick wall in general at 16khz). Smashing the dynamic range to increase volume in the highs almost gives you the highs of a tweeter with their "full range" drivers. Plus, 3" midrange drivers are never intended to play above 4-5KHz really anyway. Beyond that, there is a lot of distortion. The new compression algorithm works great here too, because Logitechs already distort the highs so badly, the differences are minor!
The X-Fi and el-cheapo speaker market are the perfect match after all. Usually spending a ton on electronics (sound card, receiver) vs speakers is considered lunacy, since speakers will account for 99% of the overall sound quality. The amount of distortion electronics produce is about 0.001% of what your speakers make! But here we find the exception--the super expensive X-Fi to make your cheap speakers sound better...assuming you had the speaker beforehand and couldn't bear leaving them. If you are combining the X-Fi and AFTERWARDS spending dimes to the dollar for bad speakers...I have nothing useful to say to you.
As for Altec Lansing...they are moving back to 2.1 setups as their flagships. Their Mx5021 is their true flagship (the more expensive 6021 is really just a gimmick with a line of tweeters). Dual 2.5"s, a 1" tweeter, and a 5.25" subwoofer. The subwoofer is the only true weakness here, being in Altec Lansing fashion, very one-note bassy and distortive, but otherwise for most music purposes are more neutral and clearer than the Promedia 2.1s.
I find Altec Lansing as the "cheaper" alternative to Klipsch, with a pro-rated loss in quality. Klipschs 2.1 flagship is now the iFi, which is at $399. The 5021s fit well right below it at $200. The Promedia 2.1 is a bit out of its league now in the 2.1 flagship sector, and its value is around $130-150, being that it is older generation. The satelites have been improved on the Klipsch 5.1 Ultra, given more extension to blend with the subwoofer better, and the subwoofer on the 2.1 PM had...its limitations both in extention and in clarity.
In the 2.0 market, its the 5020s (around $70) and the Klipsch Promedia Ultra 2.0 ($100). Klipsch is again superior but at a prorated value--both are dual 2.5" midranges with a tweeter, although the Klipsch has more bass extention being a very large speaker at 6.5 inches deep.