Pros: Awesome highs, huge and precise soundstage, great isolation and comfort
Cons: Not that easy to drive (really a con?), first few batches have poor packaging
Copied from this thread: http://www.head-fi.org/t/651654/earsonics-sm64-the-impressions-and-appreciation-thread/45#post_9195138
(Warning: broken english ahead)
(I'll borrow ljokerls review layout here)
Accessories: Because I was one of the first person to order the SM64 from Earsonics (ordered them literally 5 minutes after they were announced) I received one of Earsonics CIEM-box-thingys as a small bonus ( http://www.head-fi.org/g/i/752551/dfx-jpg/sort/display_order/ ). Besides that the accessoires are just the standard stuff you get with every IEM. Works for me.
Build Quality: Nothing to complain about here. I love this (Westone?) cable ♥
Isolation: Fit is 98% perfect for me with the included bi-flange tips. Never had any IEMs that fit so well.
Microphonics: Not really worth mentioning. Tends to zero.
Comfort: Seal is great and the ergonomic design too....so how could the comfort be? :P
Sound: I'm using a Cowon J3 with mostly flac-files as my source (soon to be supported with an Arrow 4G)
Goes pretty deep and has a good punch to it! On some tracks I even get something like a subwoofer-effect. The SM64 always deliver the right amount of bass songs need. It's not overemphasized or to shy. It's just right on the spot, very natural and precise. Waaaay better than with my old TF10 (less quantity but overall just a lot better).
Mids: After the Earsonics upgraded my SM64 the mids are more forward than before. Overall more present but they never try to steal the show from the superb bass and highs. Even tough the mids are more forward than the other frequencies, the SM64 still maintain a more or less neutral sound signature. I really don't have any idea how mids could get any more transparent than on this in-ear.
I love the highs of the SM64 with a burning passion. No, really. They could maybe be the best part of this IEM. Again, they are not emphasized or something like that, but just really really accurate and natural. They manage to get really high but only when the recording needs them to be. They can sparkle like nothing I have ever heard before. My brother has been playing drums for seven years now, and trust me, I know how cymbals sound. These IEMs manage to reproduce the sound of a cymbal perfectly. I'm pretty sure that there are just a few other in-ears out there that manage such a difficult task. They are not harsh or anything like that, but just very natural.
The soundstage is HUGE with an awesome 3D-feeling to it. One of my favourite songs has a few parts in it where you can only hear some "nature sounds" (see, there is the bad english :| ). It sounds like somebody just put a mic in a forest at night and recorded what was going on there. Anyway, the amount of details you can pick out of this sections with this IEM is just stunning. You can almost tell how many meters the birds you hear are away and how tall the tree is on which they are sitting on! There is a train passing by in the far distance and you can follow his track perfectly. I can't really put my enthusiasm in words, sry :D The soundstage is shaped something like this (borrowed that graphic from a SM3 review because it seems to be the exact same shape and amount) ( http://cdn.head-fi.org/5/5c/1000x500px-LL-5c20dead_1000x500px-LL-f5fc1cdf_SM3_Soundstage.jpg ). That shape makes live-recordings a whole new experience because you really feel like you are standing right in the middle of the crowd...you ofte even get the feeling that you can hear people behind you, which is a bit weird at first :D These IEMs are fast and precise as hell. I can't really imagine how you could improve the SM64s performance in that sector. They can handle songs like this ( http://www.youtube.com/watch?v=FpfqpE6JoH4 ) like it's a simple lullaby!
So, yeah...that is my review of the IEMs I fell in love with.
I don't really have any other fancy in-ears I could compare them with and maybe you should take my review with a tiny grain of salt, because I did not test them with any kind of electronic music at all. Mainly listened to Metal, Jazz, movie scores and Rock. The sound did not really changed after ca. 250 hours. My brain just needed some time to change from TF10 mode to heavenly SM64 mode.
Overall these are very natural and precise IEMs with the best soundstage I could imagine.
You can take Earsonics really serious if they say that these earphones are all about "Headstage and Musicality" :)