Here is some comparison with my Fitear 335SR and my Shure 846.
NB: I use the blue filter with shure olive on the 846, the bass port is colsed completely on the 2.5. The comparison was done with a Sony ZX1 as a source. I'm not an english native speaker so excuse my low level english
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Resolution: those 3 are sensibly in the same league.
Detail retrieval: slightly better on 335SR and 846 because of the upper mids and trebles more emphasized.
bass: the 2.5 and 335SR share some similarities on the bass department. Thay have very full bass. The 2.5 has however more sub bass leading to more punch, and the 335SR have slightly more midbass. The 335SR bass might be a little bit more articulated with more speed. The 2.5 have a more natural sound in the bass department. I feel the bass quantity is time to time too much on the 2.5. The 846 will best those two in my opinion. The balance beetween sub bass and mid bass is perfect, the bass get never overhelmed, the punch and texture are wonderfull and the speed is better than 335SR or 2.5. The bass of the 846 feel so clean.
Mids: the mids presentation is very different on those 3. The 846 has a "in your face" mids presentation, with the upper mids emphasized. It has a very raw texture leading to a very exciting sound. The 2.5 has a very smooth mids, the warmest of the 3, with the best natural feeling of the 3 and the most relax presentation. The upper mids are slightly seted back. Great articulation too. The 335SR is in the warm side too, like the 2.5, they have a very lush presentation. The upper mids are slightly more than the 2.5 and less than the 846. They have the most neutral mids of the 3. The articulation is great too. The mids are top notch on those three IEM.
High: the 846 have the highs with the most energy of the 3. There is still this raw and grainy feeling in the sound with an amazing texture. But they are some kind of darkish highs. The 335SR high are very refined, very smooth with great texture too. The hamonics are very easy to catch and the extension is great for an IEM. Technically maybe the best highs I ever heard from an IEM with a perfect trnasition between the upper mid range and the highs. They are also no fatiguing. There is slightly less quantity in the 2.5. The extension is as great as the 335SR but they feel slightly thiner than the 335SR trebles. Everything is there but seted back a little bit in comparison to the 335SR. They tend to pop up a little bit as the upper mid is seted down. They are also very refined trebles with no fatigue at all.
Soundstage: The 846 has the smallest soundstage of the 3, but there is a great deepness in it, and the presentation is very coherent as a whole. I really love the soundstage of the 846 because of this. The 335SR has a more laidback presentation in the soundstage, it is wider than the 846. The deep is on part. The listener position is slightly higher (the sound comes slighltly from the bottom) when the sounds is right in front of you with the 846. The soundstage is great on the 335SR but between the two I prefer by a small margin the 846 soundstage. But the 2.5 soundstage will beat those two in every aspect. The 2.5 has this insanely huge soundstage for an IEM. It gets closer to an open headphone feeling than the 2 others. There is a lot of more volume and 3D feeling in the 2.5. As the 335SR it is more laidback than the 846.The coherency on the 2.5 soundstage is top notch. It's the best soundstage I've ever experiment in an IEM, period (and I tried a lot of top end IEM).
Conclusion: those are 3 outstanding IEMs. The 846 has this very exciting and engaging sound, with this raw texture pretty unique in an IEM and this "in your face" presentation, and a lot of punch. The 846 has I believe the best bass in an IEM. The 335SR is the most neutral of the 3 (but still in the warm side), it has a very lush and reffined sound. The most articulate sound, with a little emphasis in the mid bass. The trebles are outstanding. The 2.5 (the darkest of the 3) shine with this unmatched natural feeling of the sound and unmatched soundstage. They are a very relax sounding IEM while having a lot of energy in the bass section, the hybrid design do a wonderfull job.
Technically those 3 are to my ears in the same league with different flavors. The 2.5 being far cheaper than the 2 others, it is one of the greatest value high end IEMs around her.