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.
The decision to go with adaptive over asynchronous was, IMHO, a cost-cutting solution that is bad for the end user. I've had excellent success with this product's predecessor, the Asynchronous Sabre U2, but this one doesn't work in Linux (with mpd) at all well. Jitter and stuttering aplenty, while the U2 works a treat. HIFIME reply: It works with other Linux devices, there might be settings you can change to fix this. Try adjusting buffer or process priority/niceness. This isn't directly related to async vs adaptive, but some other settings with the 9018.
Works like a charm, plug and play on both Windows 10 PC & Android 7 Smartphone. Sound quality is great, more airness, better soundstage, deeper bass, better clarity. Not day & night difference compared to the pc headphone out, but you can hear the difference, specially with a little bit hard to drive over-the-ear headphones. On the smartphone, the difference is HUGE in both volume & sound quality.
Amplification-wise, the volume is like 25-30% louder than my PC headphone out and 40-50% louder than my smartphone (Xiaomi Mi 5). I don't know if it's enought for high impedance headphones, but for a wide variety of IEM's and my ATH-M50x headphones they deliver more than enought power. Huge improvement on the bass and soundstage of the M50x, now they sound as good as they're supposed to!
I found that the sound improved by a huge amount using ASIO drivers, with Windows 10.
This DAC works well. Very good sound for the reasonable price. My old laptop's dac and headphones amp were so bad, and this is a good substitute.