I used all of the daps above, Fiio X3, Ibasso Dx50 / Dx90, and Sony F886, and i can say that Sony has a unique sound signature on its own. It's a more mainstream, fun sounding player with good bass, warm, clear and forward mids, and somewhat polite but reasonably detailed treble.
Detail : Overall F886 has a more detailed sound than X3, and Dx50, but Dx90 is a step above Sony.
Clarity : Sony, having the most forward and close soundstage has a clearer sound than Dx50 which has some slight grain on its sound, and as far as i remember it is a bit clearer than the already clean sounding X3. Having the soundstage too close to your ears positively contribute to Sony's transparency. Compared to F886, Dx90 also has a very clear sound, but probably due to its more laid-back soundstaging, the transparency does not hit you like Sony does at first place.
Soundstage : I prefer the stage of Sony to the rest, but this is quite dependent on your phones. I exclusively use headphones, not iems, and in that regard, Sony noticeably creates the widest stage from left-to-right. However, due to its stage too close to your ears, the depth is not spectacular. So to say, Sony's stage is more linear (from left-to-right) than round.
In that manner, Fiio X3's soundstage is also a bit linear ; a bit upfront like Sony (but not as much though), yet not extended to sides like Sony. Ibasso Dx50 & Dx90's stages, which i appreciate in terms of its balance, has the most round presentation. They are quite wide, and the depth is also good in both Ibasso's, better than the depth of Sony.
Extension : Among those four, Fiio X3 has the most compressed treble, and dynamics with a high freq. roll-off that begins quite early in the frequency spectrum. The bass extends nicely, but as i said, treble is quite rolled-off.
Ibasso Dx50 also has a noticeble - though less than Fiio - treble roll-off. But the bass in Dx50 does not go quite deep as Fiio, and its impact can be somewhat less than Sony and Fiio.
Sony F886 has as i've said, good, impactful bass like Fiio, and it's not bad in low-end also. Yet, none of those players I think can give the well-extended sub-bass of Ibasso Dx90. In terms of treble, Sony has some extension, but it is not again at the level of Dx90. It has a quite smooth, non-fatiguing highs, though relative to headphone, it can sometimes sound a bit harsh on cymbal crashes, and even occasionally, the vocals can be shouty.
In terms of extension, Ibasso Dx90 is the king of the four without a serious rival. You can easily hear real sub-bass rumble in many songs, and its treble has the highest, and most airy extension among these players.
Bass : Fiio and Sony both has impactful bass performance, and fortunately, their equalizers do not compress mids if you use their bass incrementation. Among four Ibasso Dx50 has the most shallow base, but at the same time it shouldn't be called as bass-light. Ibassdo Dx90 on the other side, has good impact, and it gives you the most textured bass in that comparison.
Mids : Sony has lush, transparent and very forward mids, and their warmth gives a pleasurable listening experience. X3 also has very clean, and a bit forward mids, yet the detail is not that obvious like Sony.
As I told before, Dx50 has some very slight grain in its mids, but the instruments were placed and layered better than X3 which creates a more 3D listening ambience in its laid-back soundstage.
Dx90, sharing the same 3D sounstage signature of Dx50, has cleaner mids than its cheaper brother with again good layering, and slightly better separated instruments than the rest of the players here. Yet, I feel it may have a very slight bit of V-shaped sound with again very slightly recessed mids.
Btw, the instrument separation of all these players are quite good with Dx90 having the lead by a small margin against the rest.
Treble : X3 has the most polite, laid back treble making the player a bit darker sounding.
Dx50 on the other way has a bit more detail in the treble region compared to X3, and despite again having a roll-off, it has more extension, and better dynamics than X3. But, I refrain from saying that Dx50's dynamics are not compressed ; but not as compressed as X3. The obvious compression of dynamics in X3 makes it a non-ideal player for rock as an example.
In that sense, Sony has more clarity, details, extension, and dynamics compared to X3 and Dx50 in the treble region. Yet, it also has a treble roll-off, creating a slight compression in dynamics. From the other side, Sony probably has the smoothest and easiest-to-listen treble in the comparison.
Dx90, by a noticeable margin, has the most-extended and crisp treble, and the best dynamics without any compression that I've felt. It also has the (somewhat audio-technica style) sharpest and the most aggressive treble probably due to its Sabre dacs. The treble of Dx90 is a joy to listen to with its detail level, an at the same time it can be fatiguing at times.
UI & Usability : Fiio X3 is probably the hardest to control with its UI. Ibasso's have nearly the same user experience, and operations are fast with their highly responsive touch screens. The touch screen operation of Ibasso's are even faster than Sony's which sometimes show a slight lag. But, the three front buttons of Ibasso have some lag. And all these Chinese player show more crashes than Sony. But I want to point that, I was nearly perfectly happy with the usability and UI of Ibasso's.
Sony, at the other hand, has the least amount of crashes, as you may expect. And the tactile buttons on its right side are a pleasure to use.
Battery : Generally, the batteries of these players do not exceed 10 hours in normal use. I think Fiio is around that number, or a bit higher. In fact, Ibasso Dx90 drains power very fast when listening to high-res tracks. Dx50 is better than Dx90 in that way.
You do not reach the 20 - 30 hours of use in Sony in normal conditions. Screen, searching through songs, android apps, sound gimmicks (clear stereo, clear sound, dsee, surround etc.) eat a great deal of battery when activated. But I think you can get a decent battery life if you play 16 bit files of mp3 or flac.
For any curious guys, though I miss the detail, sub-bass, and treble of Ibasso Dx90, I am using Sony F886 right now due to its very thin form factor, battery, and lush mids. I am eagerly waiting A15, assuming that it will most probably be in the same level of sound quality with F886.
