The S9 Pro dac is very small and, just like the S3 Pro dac, the S9 Pro also supports microphone input, which means you can use a gaming headset when playing online games on your computer without having to use an external soundcard as a mic input.
The S9 Pro is also perfect for high impedance headphones, which are typically low sensitivity so, they naturally sound quieter when driven from a phone. In terms of audio performance, the S9 pro balanced output has naturally better performance because it literary delivers double the output power. This makes a huge difference to audio, making the overall audio more dynamic. The bass is punchier, the higher tones are clearer and more detail.
The S9 Pro isn't equipped with a rechargeable battery; hence it's a bus powered dac that takes power from the source is connected to. The S9 Pro is equipped with the Sabre 9038Q2M chip, which is the more efficient version of the ESS Sabre 9038 chip (less power hungry than the Sabre 9038Pro), although it still draws a decent amount of power, which you will notice when the S9 Pro is driven off your phone. 
The Sabre 9038 chip is powerful and capable of 32 bit PCM audio (up to 768khz) and NativeDSD audio: DSD64, DSD128, DSD 256 and DSD512. The S9 Pro has a sample rate status led, which is designed to feedback the current sample rate, using different colors. Yellow: DSD64/128, Purple: DSD256/512, Blue: PCM176.4/192(Khz), Red: PCM 352.8/384(Khz), White: PCM 705.6/768(Khz) and Green: PCM 44.1/48/88.2/96(Khz)
The Hidizs S9 Pro is compatible with various operating systems, including Windows 7 which the S3 Pro dac does not support. The driver needed for Windows 7 can be download from Hidizs website. Aside from Windows, the S9 Pro supports MacOS, iOS and iPad OS. 
The S9 Pro dac amp comes with a short male to male USB-C cable that supports audio and OTG connection to a Windows and Android device. For Apple devices, you will need a USB-C to Lighting adapter, which is not included. Most Android phones support OTG, although not all. It's also worth keeping in mind that you won't be able to use an aftermarket USB-C cable unless it supports audio. Most USB-C cables only support charging and data transfer. The included cable weighs 5 grams and measures 9cm long (14cm including the plug connectors)
The S9 Pro weighs 12 grams and measures 6cm long, 1.8cm wide and 1.1cm thick. The S9 Pro frame is made of a single piece of machined aluminium alloy with glass panels on front and back. The S9 Pro is mostly flat, although it has square protrusion on the top front and back, which means the S9 Pro does not sit flush against a desk. As far as branding, there is a large laser printed Hidizs logo on the front, as well as large font text on the back side.
A couple of Hi-res stickers are included, as well as a USB-C to USB-A adapter and a protective case (weighs 3 grams) with a croc clip on the back. The protective case is made of thin plastic with a frosted finish, while the spring-loaded clip has a low to medium clamping force. Compared to the S3 Pro, which only has a single ended port (55mW at 32 ohms), the S9 Pro single ended port has double the output power; hence the S9 Pro is a naturally more powerful dac amp solution. In terms of footprint though, the S3 Pro wins that department. It's about the size of a coin and weighs just 7 grams. You can buy the S9 Pro from Hidizs
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