Muse is tough on the X1s I've found, especially the live ones. I believe it's the way they're albums are engineered. Also, what type of files are you using? Nevertheless, if it's compared side by side, same source, etc with your 558s, it should still be competitive. I would say the only thing would be burn in. My X1s handle Muse a bit better now after weeks of burn in.
I think you're right and I maybe just picked a bad first track (Hysteria) to test the X1s out with. After a few more hours listening to all types of genres I've pretty much done a 180 on the X1s and I'm enjoying them a lot, both amped with the E18 and just using them directly plugged into my laptop/phone. Tons of bass but all the benefits of open headphones that I had enjoyed with the 558s.
Edited by parkerlewis - 1/24/14 at 3:33pm