I've heard them side by side in J&R's in NYC, and now own the 5021s. I would say the 5021s are better at music, while the Promedias are better at games and DVD watching. Not that the 5021s are BAD at that, and not that the Promedias will make you swear off iTunes...just that they are each biased in their design to a certain niche. The dual 3" midrange drivers (and 1.5" softdome tweeter) in the 5021s mean that they can pump very nice midrange, and have a low cross-over point to the subwoofer - this is essential for good stereo imaging in music. The Promedias have more rigid speaker cones, and deal with high-volume transients better, as well as having a tougher, more directional tweeter. So they can play a bit louder without distortion. I do think the 5021s are more neutral in tone. Lastly, I like the fact that the satellites for the 5021s are easily wall mountable, and indeed come with wall mounts. I don't know if the Promedias do or not...
So I can characterize them for you, but you have to figure out your use...
Future Shock