I felt that UM3X is way too rolled off in the treble with some tips, like the foam comply. But it was fairly well balanced with silicone tips. From my experience, multi-driver BAs can change their sound greatly depending on how you fit them in your ears - too much so IMO. I think SE535 is more balanced and lively sounding, but with the wrong tips and fit, the midrange can become overly present and shouty, the highs can sound harsh and the bass can sound detached from the rest of the spectrum. UM3X never sounds harsh which is a good thing in a way and also never sounded obviousily incoherent either (although I think I could still hear the lows, mids and highs playing a bit separately from each other). But it also lacks the sparkle and fun factor that SE535 possesses. One could call UM3X more of a studio monitor, while SE535 sound is more audiophile friendly IMO. With the UM3X, I noticed that the bass, while tight and deep, seemed to suffer from some "plasticy" case resonances - it wasn't very noticeable, but there. SE535 has a somewhat better composed low end IMO, but does lack some sub bass presence compared to UM3X. Overall, SE535 is forward, lively and even aggressive sounding in the highs, while UM3X is softer, smoother, but may seem too dark and boring depending on tastes, fit source, etc. I believe UM3X has the potential to sound more recessed and veiled in the upper frequencies and more boring than the more forward SE535.
