I just got my 545s and have been playing around with them. My first impression of the sound is very positive. I only have my Clip and an ELE DAC here at home to try them with (my O2 is at work). Through the clip they sound a tad dark, but really very good. They sound even better through the ELE, which is bright so I guess that makes sense.
I don't understand the guy who complained about no bass? I hear plenty of bass. In fact, IMO it's about perfect. Thumpier headphones can be fun for some music, but the amount the 545 has strikes me as a great balance for an all-purpose set. I can see why it might even be too much for some, but I like it. The KEF M500 seemed a bit clearer and more neutral, but thinner and not as enjoyable to listen to for me.
In fact, what stands out to me most is that unlike every other set I've bought in the past couple of months, I can't point out anything in the sound that bothers me. They sound great with all the genres I've tried. I'm not sure about the comfort yet... my ears fit inside but they are touching the inside of the pads. These aren't the most comfy set I've had.
Anyway, just a few preliminary thoughts.