For long I was searching for a portable dac/amp that could adequately power some of my headphones like Sennheiser HD6XX, Sundara, AKG K7XX, DT 770 M and some others at my office or even at home comfortably without the inconvenience of a desktop dac/amp stack with power chords and other leads running around. In my experience I found S9 pro do just that without any hassle.
Provides ample volume headroom both on MacBook and iOS device. Headroom increases further from 3.5 mm SE to 2.5mm balanced output. Drives all above mentioned loads easily with enough headroom to experiment with.
Due to fast battery drain I have to use it as a laptop/MacBook portable dac/amp and on all occasions while using with iPhone have to take frequent breaks to recharge the phone.
I realised I’m using it more often than my desktop stack, that’s how clean and powerful sounding it is.
In my experience I couldn’t appreciate any difference in SQ between SE or balanced output.
Depending upon the load it gets hot from warm very early on and then remains at the same temperature throughout the listening session. I hope manufacturers knew about it and May be it can handle this much heat. My one session could go as long as 6-8 hours at times. So I guess there is nothing to worry about it.
Unfortunately, the USB C to lightening cable costing around 2k and purchased separately did not work in balanced mode output but works fine with 3.5 mm output on iPhones. I won’t count it as a negative remark on S9 pro review though. The dongle is good.
iPhone users can buy it elsewhere easily.
I liked some of its Sound qualities, very clear, low distortion and the complete silent background in between the sound passages are some of the things you might catch early on a first listen.
Imaging, soundstage, equipment separation, resolution everything is fine and is impressive but don’t know why I found the depth is missing to some extent and that its actually nitpicking at this point.
As of now I’m going to use it as a portable device for above mentioned headphones at office and at home as well but not as a on the go device.
I’m able to listen to open backs at office because of a separate room and that’s the main reason I bought it and it did not disappoint.
Good luck and happy listening to all.

I am using this HIDIZS 9 pro Dac ONEPLUS 9 mobile.I use Sony WH-1000XM3, KZ ZSN PRO X, FINAL E1000 Headphone and IEM.Sound quality is good because of the use of Dac No matter how much sound the quality does not change.I am very happy to use this Dac I am an Audiophile.

I've had the Audioquest Dragonfly Black and the Earmen Sparrow before. But the S9 Pro beats both of them; it's cheaper than both, miles ahead of the Dragonfly black sonically, detail retrieval and instrument separation are better than the Sparrow even though the Sparrow costs almost twice as much. Overall - the best value

The Hidizs s9 PRO dongle has a tiny form factor!

I have tried it only on the 3.5mm, and it works really well with in-ears and headphones.

Reviews mention that it's a power drainer for mobile. My usage has been mostly with mac and it works perfectly.
The mic on IEMs will not work through this so you will have to switch the Input on your device to the built-in mic or have another external mic attached for calls.

Have used Apple lossless music for all different types of songs and different resolutions of songs, the color has lit up accordingly.

Pros
1) Best sounding dongle
2) Small form factor
3) Balanced output
4) Light Indication

Cons
1) There has been lot of network interference sound while using it in iPhone(Need HPZ suggestion for this issue)
2) Draws a lot of power while using, have to charge the phone frequently

Conclusion
Great portable DAC, with balanced output its having absolute high driving capability for hard to drive IEM's

I bought this dongle DAC because I had a real bad motherboard on my computer and wanted to upgrade the audio. When I first used it, the volume blew me away, all my volume complaints were gone. But note that I only use 32 Ohm(114DB sensitivity) AKG K361 headphones. Yes, my motherboard couldn't even power the 32 ohm headphones at 70 percent volume properly. I used this DAC at about 6-14 percent volume now, that is how much power this has. So I will probably upgrade to better headphones too.
Enough rambling, about the sound, the sound is really revealing, it has a great amount of detail and has no hiss(nice dark background). I felt the soundstage improve a lot and the bass got a lot cleaner. As far as I can tell, this DAC does not add colour to the sound, but I'm new to all this so take my opinion with a grain of salt. Vocals seem lovely to me now, this DAC brought vocals forward on my headphones and I can hear so many more details and instruments in my music.
PROS:
- Volume!
- Great Detail
- Small and portable(comes with a clip for your clothes too!)

CONS:
- Gets a bit warm sometimes, but I've read it is normal and is a non-issue.
- Drains your phone's battery. Went from 80 percent to 65 in 1 hour of listening on apple music lossless and OnePlus 8T.

I really recommend this little dongle DAC for anyone who is even considering buying one as their secondary DAC or even as a first time DAC like I did. I had a lot of second thoughts, but I'm really happy with it. Also delivery was extremely quick, thanks to Headphonezone.in for that.

I am no audiophile, in fact I have just started journey into the world of hi-fi. I bought a Audio Technica ATH M40x as well as KZ ZSX IEM. I must say that the combination of the Hidizs S9 pro with the KZ IEM blew my mind. I cannot put this aside. As I said, I am not an audiophile so I might not be able to individually comment on just the DAC, but combined with the right pair of IEM or headphones seem to work like magic.
A few words on HeadPhoneZone. Your delivery was prompt. I really appreciate the small cue cards you threw in the packet listing the audiophile grade tracks from multiple genres.