aleXmod is a deep mod of ancient Cowon X5 DAP, adding a serious DAC chip and headphone amplifier. More info at aleXmod - true audiophile tweak of cowon i-audio X5 DAP. As you can see on the picture, its size is the same to iPod 5.5 gen 80 GB, though aleXmod is thicker.

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Its developer, Alex_Nsk, asked me to review it and provided with a sample. I tried it with a various gears and returned the sample.
DACs comparison

I tried both feeding my WooAudio 3 > HD650. Both played FLACs, aleXmod from its memory and Pico from a laptop.

Pico is more delicate and softer, has wider soundstage and better separates the instruments. Mids are slightly blurred, most probably due to the its headphone amplifier stage (see further).

aleXmod is more vivid, lively, energetic, with accurate edges and sharp attack. Mids tonality sounds neutral and very correct, bass is tighter.

Both are well detailed.

Winner – aleXmod: Feeding the WA3, I prefer alive and accurate character of aleXmod over the softened and laid-back sound of Pico. Pico > WA3 > HD650 combo sounds boring in comparison. I do not think this is an exclusive fault of Pico, but rather a result of wrong combination of gear where all components are warm and relaxed. Thanks to aleXmod, I decided to upgrade my Pico to another source.
Standalone use
HD650: aleXmod vs Laptop > Pico

Blues: Pico wins Eric Clapton "Walkin' Blues" for microdetails, realistic guitar and voice.
Hard rock: aleXmod wins AC/DC "Fire your guns" for drive, energy and aggression.
Symphonic metal: Pico wins Nightwish "Dark chest of wonders" for separation and voices.
Trance: aleXmod wins Indoor "Camel" for speed, sharper instruments images and positioning.
RE0: aleXmod vs Laptop > Pico

Blues: Pico wins Eric Clapton –"Walkin' Blues" for microdetails, realistic guitar and voice.
Hard rock: Pico wins AC/DC "Fire your guns" for microdetails, separation, voice, depth, realism.
Symphonic metal: tie on Nightwish "Dark chest of wonders".
Trance: aleXmod wins Indoor "Camel" for focus, attack, clarity and separation.
ER-4S custom tips: aleXmod vs Laptop > Pico

Pico wins just because aleXmod > ER-4S were sibilant and somewhat harsh. I do not really think it is aleXmod fault, but rather a case of bad synergy, since ER-4S is prone to sibilance itself.
BLOX TM5: aleXmod vs Laptop > Pico

aleXmod is a clear winner and has excellent synergy with TM5, adding nice focus, attack, separation and sharper images to full-bodied and somewhat warm sound of TM5.

Summary notes on standalone use

Pico vocals and acoustic instruments are warmer and more detailed. This provides more realism and better sense of presence. I believe that its amp is the reason, because I discovered the same effects feeding its line-in with aleXmod headphone out. I think that these extra warmth and details exaggeration (dynamic compression?) are questionable at times. But they are safe and forgiving with the most records and headphones.

Pico better separates instruments and reproduces complex congested music.

Pico is more powerful, though aleXmod volume is adequate. Listening to aleXmod > HD650, I has 14 dB headroom above normal listening level.

aleXmod provides more lively, energetic sound with sharper attack and better focused instruments. This is good to many headphones, but bad to some others.

Winner - Laptop > Pico: it wins for the extra power, slightly higher resolution and steady compatibility (not synergy) with various headphones. All these sound benefits are small (say 15%), so some may prefer extra portability and convenience of aleXmod. Moreover, aleXmod sounds better with some headphones or music.

Note: KSC-35km clip-ons are my own creature (KSC-35 kostalex mod), described in my Best clip-ons comparison.
RE0, KSC-35km: aleXmod vs Sansa Clip

There is nothing to compare, aleXmod wins hands down in any terms. The SQ gain is so great that I can bear with its much bigger size and less convenience, when walking with the baby carriage. But unlike to the Clip, I would not keep aleXmod in my messenger bag all the time just for occasions, because it is too large and heavy for my small bag.
RE0, KSC-35km: aleXmod vs iPhone vs iPod 5.5 gen headphone out vs iPod 5.5 gen line-out > Pico DAC/amp

Even being amped, both iPod and iPhone yields much to aleXmod in resolution, details and instrument separations. aleXmod sounds more realistic, emotional and involving. Without amping, iPod and iPhone give up the power also, sounding quiet with KSC-35km sometime.
Conclusion

aleXmod is a great DAP and nice source for some rigs. Being used standalone, it may shine with many headphones, though may fault with some another. I probably would not buy it mostly due to my personal listening habits, which are better satisfied with stationary DAC, large capacity iPod (to be upgraded to 240 GB) and ultraportable Clip (to be upgraded to Clip+). aleXmod with its limited 32 GB capacity and reserved portability may receive just a minor share of my listening time. But I can easily see how well it may satisfy other people with different lifestyle.

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