mj_roseberryBetter! The ATH-M50x bested the L1's. I gave the L1's away to my neighbor. The K553Pros bested the ATH-M50x and I'm selling those on Amazon used. Does this answer your question?
The K553Pro is fantastic for the money and really great period. Versus the L1, the K553 is more dynamic and the bass is better articulated. The sound staging, which improves the sense of space around instruments and therefore improves fatigue, is quite a bit better than the L1. The L1 has a 40mm driver and the 553 has a 50mm driver.
Both the L1 and the K550 (the 533's predecessor) are on the Wall of Fame over at Innerfidelity.com. You could probably sell your L1's for a fair price if you want to offset the cost of these new K553 cans...
Hope this helps. Let me know if you need more info...