I have a pair of Shure SE535 for quite a while. Until now, I've used it for my mobile phone. The sound quality:
+ good mids
- rolled-off highs
- weak soundstage
- practically no bass
My phone outputs 32 ohm and uses lossless files. Those facts made me think the phone couldn't be the cause of the disappointing performance. While these IEM's are still many times better than regular earbuds, they were not that impressive for $500. I felt that Shure SE535 was overrated and over-hyped. I was already thinking of selling it.
That is, until I tried them on my Little Dot MK III headphone amplifier. I used a gain setting of 3 on the amplifier and connected it to my high-end CD player. I experienced jaw-dropping fidelity on the SE535 which I didn't expect. The highs were more noticeable, the instrument separation became very direct, the soundstage was much much better and the bass was deep and punchy. I had no idea that the SE535 could actually do this. I used different genres such as rock, bass-heavy music and pop music to notice the differences. It sounded very similar to my audiophile full-size open cans. Full-size cans are still better of course, but the SE535 really had the same style of sound. It could not be compared to sound coming out of my smartphone. On a serious headphone tube amp, the SE535 is so much better that smartphone output is a joke. The SE535 is notorious for having a serious lack of bass. It's the Android/iPhone's fault. The SE535 has very impressive bass when amped on a good tube amp. Very deep and rich.
If your SE535 sounds mediocre on your mobile phone, trust me, it's your phone, not the IEM's. I thought the SE535's were overrated. I felt ripped off and wanted to sell them until I heard the capabilities on a decent source and serious headphone tube amp. The SE535's are stunning IEM's and not overrated at all. It's just sad that it's too good for a smartphone. Because of these IEM's I found out how bad the output of smartphones is. I ordered another pair of IEM's that have more soundstage and bass. They are on the way, but I might return or sell them, because the smartphone is the bottleneck. Even if I'd buy a $1000 IEM, it would still suck on the smartphone. I'm keeping these SE535's.
On a good portable audio device, these IEM's should sound better. A smartphone is simply too weak and not worthy of such an IEM.