They arrived at my door about 40 minutes ago and have been in my ears for about 30 minutes. I immediately put the custom UM56 tips on them. The first thing I noticed about the E500's is they have a slightly longer barrel than UM2, which makes for a nicer fit with the custom eartips, seems like a more secure seal with them, more comfortable with them as well. I'm using a Sony NW-HD5 and a Larocco PR II amp with OPA627's. I've noticed they're more detailed than UM2, making the UM2 seem almost muddy by comparison. The instrument separation is better. There seems to be a little less bass quantity, but it's a lot tighter and seems maybe even deeper. There doesn't seem to be any hump in the upper bass. Mids seem more apparent than UM2, which was something I was really hoping for. The highs don't sound recessed at all to these ears, especially when compared to UM2. Anyway, I'm sure the sound will improve with burn-in, and keep in mind, these impressions were made with the UM56 tips, and with UM2 I found that they made them sound distinctintly different than any of the stock tips. Anyone who was thinking of getting UM56 tips for these babies, I would recommend setting up an appointment with the audiologist now. The fit of these is even better than with the UM2. I think Shure really outdid themselves with the E500.