The bass on the SINE has more detail and presence, especially if you struggle to get a seal with the Elegia. The mids are more resolving on the SINE, more forward and more natural on the Elegia. The Elegia has wider soundstage, but it's still pretty typical of an closedback. Treble on the Elegia is more present and more prone to peaks. The SINE is more polite, but also smoother in the treble. They are about even in separtion and imaging. The SINE is much more capable of taking EQ without distorting and getting to high volume without clipping. The SINE are more secure on the head and more premium in build, but they clamp your head like you killed their father. The Elegia more heavier (or at least feel so), but they sit well on the head. However, they are very prone to frequency responses changes depending on positioning and seal (which can be difficult be get right).
More subjectively, I'd take the Elegia for vocals, and the SINE for everything else, particularly bass heavy music. I'd take the Elegia for comfort, but the SINE for portability. If you like to tinker with EQ, it's the SINE. If you like to pad-roll, it's the Elegia (but some folks on this thread have pad-rolled the SINE with some apparently excellent results). Overall, if you can put up with the clamp, the SINE is IMO is the better headphone for sound quality.