I am currently selling my ps500 to buy back the ms pro in order to do that exact comparison! I somehow think the hd600 may top ple it off it's perch as my face headphone ever as there is nothing the hd600 doesn't do well - it is probably the greatest all rounder ever and it smooths over bad recordings in a way that the grado variants don't so if you hate sibilance, as I do, then its hd600 all the way. That being said the ms pro has its advantages as well - minimal amping requirements and great energy but yeah after extensive searching I think these are my top 2 headphones long with the dt250/80 as a closed option - once I have the ms pro back in the collection I think that will be it for the experimentation for me. But sometimes I wonder if should even bother getting another pair of ms pro at all since I enjoy the hd600 so much and would be perfectly happy with them as my number one headphone - but curiosity is getting to me and I feel I need to do the compraro to find the one headphone to rule them all :-)
Yes, the mspro sometimes would sound too dry compared to the HD580 in my system, but other times it is so damn energetic... Electrical guitars are so amazing on the mspro, I think they are both great headphones, but HD580 is (cheaper) and more suitable to different types of music.
I'll ask for more people's opinion in the upcoming meet in Sydney!