I demoed the HE-500 before I bought the 1540. I listened to a small selection of songs for about 10 minutes. I would say that they were comparable in their detail and sound signature. Maybe with more listening I would have picked up on the nuances between both of them, but beyond the imaging I would be perfectly happy with the 1540 over the 500's. This is especially the case if you are looking for a light closed headphones with a darker but detailed sound signature.
One thing you notice with the 1540's is that the sub-bass is where these headphones shine. They produce a sub-bass that really brings some weight to any music you listen to without drowning out the rest of the frequencies. I don't find that the bass is ever bloated, it is detailed and fast.