Pros: Sound, build quality, replaceable battery, portability
Cons: Bad UI, lack of USB DAC driver for Mac and 64bit windows yet
Lets talk a little on my background. This is my first review, any comment would help me to improve.
I joined orchestra and school band in my high school age, playing brass instrument (B flat trumpet), play piano to Grade 5, not to say a pro player but I then learn to appreciate music, all kind of music.
More of a mobile user, so I won't be reviewing the amp section as I use IEM on my daily basis. The only headphone I had was Denon AHD2000 and Audio Technicha AD700 which is pretty easy to push, any player should have them played without issue.
I had currently three IEM left in inventory but only paired Westone 4 and Xiaomi Piston with DX90. Ficher Audio DBA2 MK1 is with my brother so I have no chance to test with it yet.
Personally I don't believe in burn-in hype so I did not leave my player playing songs overnight. Current up-time is around 24 hours on and off.
Owned DX100 before for almost 2 years but I sold it for Dx90 for its portability. Didn't do it on purpose, initial plan was to get iRiver AK120. Sold a few weeks before I learn about DX90.
Since Dx90 should fall under a portable device category, it is fair to say that Dx90 is quite portable.
Dx90 rated :
Case dimension: 2.52W x 3.98L x 0.67H (inch)
64W x 100L x 17H (mm)
Weight: 140g or 4.94oz
While Dx100 is obviously bigger than Dx90, HM602 rated :
Size: 62mm*103mm*26.5mm or 2.4 * 4.05 * 1.04 Inch
Weight: About 200g / 7Oz
which is just a little bit lighter than HM602, and a little bit thinner. AK100/AK120 would be the most portable player I have learn so far.
Physical buttons of Dx90 is not bad by far, three buttons on front panel (Back, Play/Pause, Forward), power button and physical button lock on the left, volume up-down on the right, gains toggle on the bottom. The output jack and input jack seems to be better quality than dx100 and hm602. iRiver AK lines is still winner on the design, but dx90 is not left by far.
iBasso rated Dx90 could operate 8.5 hours, Dx100 7 hours, HM602 9 hours, AK100 16 hours and AK120 14 hours, but the user replaceable battery still makes Dx90 a potential winner as we can prepare as much battery as we need while in travel.
User Interface of Dx90 is a love-hate situation for me. It is simple but that lacks of easy retrieval way of information, that includes making navigation a hassle sometimes. This could be workaround by using shuffle mode and a playlist but I have no problem with AK lines' UI. Button is too small, so as the screen. Coming from Dx100 and iphone 5s makes me feel that the screen is too small for touch screen navigation. Although the UI response time is better than Dx50 but I think it could be better. Scrolling the folders lead to accidental "click". They need to improve the UI in future firmware or else someday people might exhaust on trying to navigate a song.
Another big problem is with the firmware. I have no problem with the scan time, it is improved due to a different hardware implementation (eg dual core cpu), I have no problem either with how it can only charge and listen with a charge only usb cable. Listening is not allowed when your pc is accessing your dx90 storage. but I have a big problem while they released the USB DAC feature without 64-bit and Mac drivers. (yet. customer service replied that 32-bit driver is added but never mention anything additional to 64bit driver and Mac driver). Sometimes song will be cut off after 1-2 seconds of play, back and forward button will sometimes delay 1 second+ as well, but that shouldn't be a big problem as that doesn't affect its core - Sound Quality.
The best part of Dx90 is the sound quality. Despite of those Firmware and UI bug, it is indeed a very good sounding dap, for its implementation Dual ES9018K2M, each for left and right. Despite of the technical specifications 8 core vs 4 core (ES9018 vs ES9018K2M), I think the Dx90 sound quality is not far behind Dx100. Some song sounds better than Dx100 indeed, to my favour. Not far behind from AK120, but the most important thing to remember, they all sound different. This dx90 is definitely sound better than HM602 to my liking, the dx90 is spacious, I cannot say it is lack of soundstage, they are big indeed but you're like sitting very close to the performer. The "live" performance is happening quite near to you. The instrument separation is good, you can easily differentiate what instrument is included in the recording.
One thing special about Dx90 is you can imagine (or listen to) quite a lot of the ambience. You can listen to the piano sustain pedal, clarinets and oboes tick-tocking pad hole, you can listen to the air hissing in the background, don't be surprise if you did not listen this on other dap, it might not be your faulty dx90, but it is just resolving some adds.
Sound stage, using Family - DreamGirls soundtrack (16bit/44.1khz), Mahler Symphony No.5 (24bit/192khz), Hotel California - The Eagles (24bit/44khz), Skyfall - Adele (16bit/44.1khz).
in the track Family, all singers are singing in the same position, or slightly close to each other, this is defer from what I've listen from Dx100. Dx100 sounds as like singers are standing far apart, which is different from the movie. They should position quite close to each other as like in the original movie. For Mahler Symphony No.5, instruments like trumpet shines, bright and outstanding; Cellos and double bass goes extended deeper, it sounds quite similar to the Dx100 in this aspect, just that Dx100 has a better dynamic.
Things were comparable on AK120. I can't really differentiate their difference on sound stage and dynamics, but different sound signature, yes. On Hotel California, the guitar in the beginning were almost as sweet but the bass afterwards coming in sounds different. AK120 does not decay fast, makes a good echo of the floor tom (I believe it is floor tom), Dx90 and Dx100, that tom sounds tight. Less there are. Overall sound signature for AK is warm, and thick. Dx90 sound neutral but not flat. That quickly judge when The Eagles start to sing, focus immediately goes to the singer without a blur line there. The Eagles sounds equally nice on AK120, DX100 and DX90, but the backing singer were more precise on harmony on DX100 imho. Followed by Dx90, they make a very good harmony by not outstand each other. On AK120 the backing singer is really sound backed, they positioned a little bit behind on the stage.
The volume of AK120 easily become shouty at above 55. I'm okay with Dx90 at around 205-210, it is become too loud when Dx100 reach 205. The 255 step volume controller is for me more precise and nicer to use. instead small changes on volume for AK120 makes big difference of volume in my opinion. Adeles' Skyfall needs a bigger soundstage, as for me DX100 is superior than both AK120 and Dx90. I cannot really tell the difference on this track other than different sound signature and texture, especially when Adele sounds equally perfect in all dap. Only thing I wish to listen more strings instrument in Dx90 than those brass and percussions. String instruments are important don't you agree? In AK120 and Dx90 i felt that the strings is overwhelmed by brass and percussions, which in Dx100 it is quite perfect for my liking.
Other quick listening session on A Great Big World - Say Something, John Legend - All of Me, some old Japanese song like Nada So So, XJapan - Kurenai/Crucify your love/Art of Life, some nasty mandarin songs that have simple chords, piano master like Yiruma - River Flows in You, Kiss the Rain, The Letter, sexyphone Kenny G, and much more, DX90 is a good companion for many genre. It justify the price of $419, and for its portability, it can be used everyday. Waiting bus/train, in a library, dinner alone, shares music with your loves one, it justify most of the situation where a dap is needed.
I only owned one player which is HifiMan 602 where the price range is suitable for comparison. Dx100 is good but for that size and weight it should be a desktop rig rather than a portable rig, and is price at $829. AK120 is almost 3 times more expensive than Dx90, but provide better UI and Firmware, slightly warm sound signature, and equally portable compare to Dx90. If you have budget and crave for sound quality you should really go to AK120.
My personal favour (only SQ is considered)
DX100 > DX90 > AK120
My personal favour (all elements are included, exclude price )
AK120 > DX90 > DX100