I must say that the Merlin demo does not fit my ear very well so I have to press them against my ear to listen to them well, while my se846 is using custom ear tips which are really doing a good job.
First, the most noticeable difference is the soundstage. Shure has a very special soundstage of focusing the middle and putting all the rest in the side, you may easily find a gap between the middle and the side. And the Merlin shows all of them on the stage at the same time. The se846 gives you a feeling of a studio size soundstage and Merlin gives you a concert-size soundstage.
Secondly, the mid of the Merlin is a bit laid back than the se846, and I must say Merlin sound more bright and cool while the se846 is very warm and intimate which I believe is the shure signature mid,I find that unresistable in listening to studio recorded pop.
And the bass, Merlin has a very honest bass compared to se846 which I find is often exaggerated. The depth and control of bass in Merlin is also found superior to the se846.
And for the high, Merlin simply is more extended than the se846.
However, I shall conclude that even Merlin has a better soundstage, and qualitatively better bass, the mid and quantity of bass in se846 really defines itself,I wish I could own both.
Ps. The dynamics of Merlin outshines the se846 a lot and the Merlin is definitely recovering more details. The Merlin sounds more honest and the se846 is more slow and musical.
I must say, the Merlin strongly resembled the properties of HD600, but with more clarity, details, but less bass