Adding Tone Controls?

My system sounds wonderful when playing well recorded jazz, classical, or "audiophile approved" material. Unfortunately, mass market pop frequently sounds horrible, with screechy splashy highs. It's obviously recorded with a built in bias to be played on car radios or lo-fi mp3s.
What can I add to my system to tone-down the highs on this sort of material? Sure, there's plenty of well recorded material to listen to, but there are plenty of pop rock bands I'd really like to explore if the recordings could be made a bit more listenable.