I've just received my SM64 today from SONVIDEO in France and I have to say I'm a bit disappointed. I've struggled to achieve a good fit with the bundled ear tips so I had to place an order for the phonak audeo ear tips as suggested by eric, which will be arriving next week.
Upon opening the package, I played around with it for a bit by removing the detachable cables in order to fully inspect the housing for any faults. I'd forgotten which cable colour (red or grey) corresponds to which monitor (left or right) so I just inserted whichever cable colour into whichever monitor sounded best, which was (red cable with the red side facing down in the right monitor and the grey cable with the grey side facing down in the left monitor). Please let me know if this is the correct corresponding cable to monitor insertion as the cables are not labelled left or right.
I'm coming from the Shure SE535 and the Sony XBA-A3 paired with an unamped iBasso DX90 and 16bit FLAC files. Both IEMs sounded great out of the box, but the sound out of the SM64 leaves much to be desired. With the iBasso DX90 on high gain and 231 volume, it sounds slightly thin and grainy. The bass occasionally hits hard and low (when I get a good seal with the lousy double flange tips) but most of the time sounds thin. The mids are fairly decent and not recessed, but sounds grainy and unrefined in comparison to my SE535 and XBA-A3. The treble sounds very well extended and somewhat detailed, but there is still an element of grain to the sound. Sound stage sounds decent with good depth but isn't close to the width of the XBA-A3, imaging and separation is excellent, I'm already picking up on some details missed by the XBA-A3 but the overall sound is just not currently pleasing or perhaps I had an inflated opinion of these based on the many positive reviews that I've read on this thread.
Another thing to note is when I first inserted the IEMs into my ear after confusing the cable to monitor connection, they sounded incredibly thin and grainy (like 5$ earphones), then shortly after with a few more insertion attempts they sounded slightly fuller but still with that thin bass and grainy mid/treble. An hour later (brain burn in or actual burn in), they sounded slightly more fuller and less grainy. Right now they sound pretty decent but there is still an element of grain/unrefinement and a thin low end which I don't like. So I've cast them aside to burn in non-stop with my iBasso DX90 until I receive the phonak audeo tips and decide whether I will be keeping these or returning them. I want to love them and settle for an affordable sub 500$ end game IEM, but these just don't currently sound like a sub 500$ end game IEM.
Suggestions are welcomed, of course. I have one of the newest batches of SM64 because my cable connectors are clear as opposed to the black seen on some of the SM64s on this thread and my earphone jack is also grey and smaller in comparison to the black and larger jacks that I've seen of previous SM64s. Also, my box came with a larger selection of tips (all rubbish) as opposed to the limited selection that some others have received.