So one of my front speakers is cracklin' its way to an early grave (the third of the four in the original set), so it's time to replace 'em. (I will eventually pick up the matching center, but not just yet, 'cause my TV died too! Stay tuned for THAT thread. ) Use is mainly movies and TV, but also music. I'm kinda tempted by the new RP-600Ms, but I'm not sure if there's a place nearby where I can hear 'em. They replace the RP-160M, which are currently about $200/pair cheaper. The tweeter seems to be substantially different, but I'm wondering how much of an upgrade the 600s are. Has anyone here compared the two? Are the 600s worth the extra cost? What about the RP-500M and RP-400M? How different are they?