After 3 1/2 hours of listening to all digital music via mp3 fed through my Mac, Wow. Just wow. Going from Infinity bookshelves to these things is like nothing I could have imagined. I realize they aren't exactly Diamond 800's, but they're far superior to anything that I've ever owned, or heard live and in person. Since I got the sub pretty well tuned in with the Mk3's, I haven't really moved off of my recliner to dig for records. I'm kinda stunned. After only a few hours with these boxes, those terms I've always only heard such as: "soundstage", "imaging", "depth", "insert other audiophile-ish words here..." seem to carry some meaning to them!
Now the techy side:
The Mk3's sound like they begin to roll off around 50hz. There's somewhat useable bass below that, plus the bass down to that point is strong and clear. I've set the LPF on my sub to 50hz (lowest setting), it's a 24db slope. All things considered, this puppy should put out the business loud and clear all the way down to the subsonic filter at 18hz.
And I'm seriously listening to Rhinestone Cowboy at 3:46 am!