@plaw -- "...Only happens on some songs."
So, you really like your speakers but have a few songs that sound screechy. It's no secret that there are albums out there that just aren't well recorded. Or, they were mixed and mastered using studio monitors that had different characteristics than your Wilsons -- things sounded perfect in the studio and not so perfect on your system.
That's an inherent dilemma with ANY stereo -- sound quality is always dependent upon the recording. A system that sounds great with some recordings is not going to sound that way with others. The one possible fix is to be able to adjust equalization, but that also has drawbacks -- another component in the chain, and the hassle of changing the settings with every new album or song -- at some point, most people want to listen to music instead of putzing around with adjustments.
Odds are that if you change speakers so that the harsh recordings sound better, you'll end up finding other recordings that used to sound great no longer have all of their magic.