Just for fun I tried swopping from the usb cable from laptop to a Teac UD-501 to the UAE23HD and optimal cable to the toslink input of the Teac and that is now its permanent placement. Compared to the USB solution, sound stage and ambience is now in another league.
I was shopping for an inexpensive USB DAC for my my laptop/Spotify setup when I stumbled across a review of the Sabre 9018. I was running the headphone jack into my Nobsound HiFi 6J1 Vacuum Tube Preamplifier > TubeCube | 7 Stereo Vacuum Tube Amplifier: an awesome little 3.5 watt tube system ($225 total + tube upgrades). It sounded great, but instrument separation/definition and soundstage were lacking. It was also a bit harsh to my ears.
This is the best $70 I've ever spent on a music system. Hands down. All frequencies are smoother, yet clearer and more defined. Bass sounds much fuller and more rounded; treble is crisp, but not harsh. But, I'm amazed at the difference in midrange vocals. This is where things really bloomed. The DAC also completely eliminated a bad hiss I got from the headphone jack.
The Sabre 9018 DAC has brought my system very close to the warmth and clarity of my Music Hall MMF 7 turntable. I'm totally satisfied with this product and will recommend it to others!
I use this in office with my work laptop and a pair of iLoud Micro Monitor at very low volume. Makes the speakers come alive, and me glued to the table. Very good details, wider and a bit deeper soundstage, bass is extended and hits lower. Good dynamics and micro details. I know I nail it with this DAC as I'm just glued to listening compared to before I just constantly wanted to tinker with the setup to improve sound.
I have used 3 other DACs with this setup so far. Fiio E10K which sounded more polite with less dynamics and bass. Dragonfly black v1.5 which sounded as good as this Es9018k2m but with graininess. And also Mojo which sounds very very similar but let's just say more controlled but by no means lacking. Overall I think I just prefer this ES9018K2M. It just makes the music feels right.
One thing to note however is EMI or RFI. I have to find some shielding.
I'm new to stand-alone DACs and wanted one for listening to my FLAC collection without having to go through my computer's old ESS soundcard or having to burn to CD for listening on my component system. I settled on the affordable Sabre 9018. It sounds amazing with my Denon AH-D2000 headphones and drives them nicely with computer volume set at only about 30%. Lots of power to spare. If it ends up sounding even better after burn-in, I'll be smiling! I haven't tried the optical output yet but look forward to hearing how it does directly into my component systems. I have neither 'golden ears' nor experience with other DACs but I'm very happy with this purchase. A great value for the price.
To David regarding using the adaptive mode 9018 on Linux... I use Linux on Intel, Android and on Raspberry Pi with many HiFimeDIY DACs, the only difference I found was power consumption, the Async one does sound the best I agree, but I couldn't drive it with some Android devices I think due to power, whereas the U2 and others worked ok from Android, although I get stutters with the 9023 U2, which could either be power or just a bad instance of this model. This Adaptive mode 9018 worked on all my Linux devices with no hiccups, I'd say it's not Linux, but most likely the particular instance of the product, it may need to be returned and replaced.