There are lists of DIY-er out there who provides a decent mods for their players. A few of the famous one are Red Wine Audio and Mezzo Soprano.
Few weeks ago, I sent in my Ak100 to be mod by Mr Phanom from Mezzo Soprano to do a mod of MSAK100S. And turns out to be a great player for me and its really a great leap from the stock Ak100! 
Would like to share some of the reviews from the mod. Its really something that need to be shared.  

This is the website for the specification of the mod : http://www.mezzohifi.com/
Nowadays, the available mods for Astell&Kern Players mostly is on bypassing the impedance and swapping of the DAC chip. 

At the early of the story, I approached Red Wine Audio to enquiry about the full mod for my Ak100 which is the RWAK100S. But the mod itself will remove the volume knob and restricted it as a standalone DAC and cant be use individually as a DAP. This bugs me as I always carry my AK100 to anyway as a DAP itself. Luckily I bump into Phanom from Mezzo Soprano which he will brings the best from the both world! I can bypass that annoying 22ohm impedance, upgrading the WM8740 DAC to WM8741 WITHOUT sacrificing the volume knob and it still can be used as a DAP! And also a digital filter is being added where you can alter the sound of it. 

Without any concerns, the decision is made to send the unit in for Mr Phanom to do the mod. 

The modded MSAK100S with the digital filter and a pretty handmade pouch from Mezzo Soprano.  
 
The Magic of the Mod
After mod, you can obviously hear the mids and highs shines out and not being recessed by the 22ohm impedance anymore. A smoothen mids and a much extended highs with a tighten bass compared to the stock Ak100. I sold my portable amp after doing the mod as I dont need it anymore, the MSAK100S alone is already doing its job well enough  
The whole clarity and transparency is significantly improved due to the WM8741 DAC upgrade. 
The soundstage has became slightly wider.
And something impressive from this mod is the musicality and the dynamic improvement from the stock AK100.

The digital filter is something fun to play with as the filter off is the minimum phase soft knee and when turning on will brings it to minimum phase apodising filter mode. 
When the digital is turned off, the vocals will tend to be sweeter and shines the strings of the music. Its like emphasising the beauty of the mids and the whole soundstage will be more airy. 
When the digital filter is switched on (The red light is on), the music will become more focused and the bass will be tighten. This narrow the soundstage but delivers a better impact at the lows which is suitable for rock or pops.

I tried to compared this side by side with Ak120 from my friend. Somehow, the MSAK100S cant surpass the clarity and cleaness of the sound from Ak120. But, the MSAK100S delivers a dynamic and musicality which is absent in stock Ak120. Didnt have the chance to compare it to Ak240 though. However, its a brilliant mod had been done to my MSAk100S. They also provide mod for Ak120 too, which I am imagining how well Ak120 will sounds even more after the mod!
For my MSAK100S, I would consider this as a best mod available for my Ak100 and highly recommending it. 

Packaging


 
The packaging is somehow not something really impressive, a thick carton box. Package includes:
-    Shonyun 306A Portable Amp
-    A Charging Adaptor (3.5mm large pin like the Nokia 3310’s)
-    User Manual
-    Interconnect Cable
 
Build Quality

 
The side by side comparison of the Shonyun Amp and the Iphone 4s. It is just about the size of the Iphone which would have a nice grip on your palm. (Dimension : 11.5cm x 5.8cm). The whole amp is built with solid metal casing with the faceplate that has the logos and the wording on it. Personally, I think that it would be great if Shonyun may do some re-design for their wording and the logos for this amp or plate it with simple carbon fibre surface with their branding on it. 
The faceplate itself would be in a blue light when it is turned on and red light while it is charging. A fully charged Shonyun may last for about 8 hours.

 
The Shonyun 306A has a 2cm thickness. Its quite thick but still not considered as bulky and is suitable for portables.

 
 
The amp comes with the normal 3.5mm headphone output port and input port along with an extendable volume knob at the top part of the amp and the Charging port is located at the bottom of the amp. There are no gain switch and power button for this amp.
 
 
 
Key Features

 
Extendable Volume Knob
There are a few interesting features in this amp which really fascinates me.One of it is the extendable knob which it will be bounced out with a single click.The knob is firm and steady and this features avoid me from sliding the volume knob accidently when it is in my pocket.
 
Auto On/Off Mechanism 
Another feature that comes with this amp is the Auto On/Off switch which will switch on the amp when you plug in your headphone and switch off when you removed the jack from it. Its an very interactive feature  would safe you from burning your battery by forgetting turning it off.  
 
 
 
Initial Impressions
The first impression when I got this amp. The faceplate of the amp is somehow not really suitable and I am doubting about how well would this thing be? The first thing I did with this amp is plugging in my custom JH-5 and sourcing from my Fiio X3 to give it a try. The only thing I can hear from it is the harshness of highs and the sibilances everywhere.This might be a sign that this amp is actually too powerful. Then I tried it with my ATH M50. Well, its another different story again. Although the ATH-M50 is a low independace headphone but it does not face the overstriking problem for the IEM. After that, I tried it with some high ranged headphones like HD800, ATH-W5000, Beyer T5p. I am amazed by how well this little portable amp can drives a big can.
 
 
Sound Quality
Gadgets involved :
Fiio X3 as source
Jh5, RE400B, ATH-M50, HD800, ATH-W5000, Beyer T5p
Copper Colour OCS Interconnect Cable
 
Sound wise, this amp is categorized as neutral sounding. The highs are being ariculated adequately, the mids we can notice a better clarity, more presence and improved smoothness.
The best part is at the bass part where there are increased of tightness and impacts on the lows. The soundstage is being widen but not very significantly. 
However, it is suggested that Shonyun 306A should not be paired with low independence IEM unless with a 75ohm adapter. 

 
 
The best part about this amp is how well it can drives big cans like HD800, ATH-W5000 and Beyer T5p like any other desktop amps. This amp is a very powerful amp that can feed these big cans. Usually I would need to use amp with power source while trying with HD800 and ATH-W5000. But this little Shonyun can drives them very easily. It’s a perfect amp for headphones which always hungers for power.
 
 
 
 
Conclusion
A very good and neutral pairing amp for mid-high independace IEM and all range of headphones. The capability on driving some big cans makes it a very worth trying amp around. Shonyun is a brand that worth a look into it and hope they can improve more on this amp by adding a gain switch that might fix the problem of limitation for low independence IEM and a redesign of the faceplates.