Hmmmm, really? I find the Sony X to pair with them amazingly well. They sound unbelievably good with it. I've been content with the combo for over 6 months which is quite a rarity for me.... and more so than any other IEM I've had with the X. But perhaps the J3 would sound even better, I don't know. I do intend to pick up a J3 at some point. But the X is by no means something to shy away from with the SM3's.
I don't know about the X haven't tried that combo yet I have two of their lower models which are warm. To SD congrats on your J3 purchase, -runs off to pair the S with the X
, this could take a bit, being one state over...- IDK last time I heard the X my impression was it is a little less warm them most of their devices but not much.