I assume that was a typo, and you're asking about the Adele headphones. What I find interesting is how different people perceive the sound on the same headphones. I really like the SM 64, it fits me great, has detailed, open sound. The one problem I have with them is I don't find the bass to be adequate. I find the bass to be good quality, but any time I have to listen to music and try to focus to hear the bass, to me that's insufficient bass quantity. It's very interesting how different people report so differently on the same information. Is it hearing difference, sample variability?
Apart from personal preference and perception, I guess the difference is mainly caused by the high impedance. SM64, to me, is an IEM which is difficult to drive well. I was not very impressed when I first listened to it using an iPhone. I was still not very impressed when I used it on an iMod with the UHA-6S MKII amp. This changed when I plugged my SM64 into WA7 - much more detailed, and finally some nice bass (sufficient in terms of quantity). I almost decided not to sell it - but then at that time I really needed the money to buy a CIEM
Nonetheless, I agree with you that I would prefer SM64 to have a bit more bass (that's because I prefer a slightly bassy sound signature) - and this is where U8 comes in