For me the SM64 fits better, but the S-EM6 isn't an issue. The shape is made to accommodate a large range of ear sizes, and my ears are big, so the fit isn't ideal, but I could learn to live with them no problem. I doubt I could say the same for the K3003, for example.
Per EarSonics, it was discovered that the original S-EM6 run had a series of small problems. They have improved the manufacturing process and increased testing and the Crystal version performs as intended. The differences between my original S-EM6 and the replacement Crystal are significant. With the original, some treble instruments were pushed very far back and the sound was dark and just different; not what I was expecting. I preferred the SM64 sound signature by a large margin. The new S-EM6 is noticeably superior to the SM64, and even the EM4 in many ways.
What can you do if you are a S-EM6 owner? Fortunately/unfortunately, depending on how you look at it, you can send your S-EM6 back for testing, and if there is an issue they will replace it with a Crystal that is functioning properly. Dealers can send them back for you, but you will have to work out turn time with them.