I'll give an initial review here and update in a week or so.
Right out of the box I can tell this is a great implementation of the Sabre 9018 chip, I already own a HiFime Sabre 9018 USB DAC with isolator and can tell the UDA18 sounds better, more integrated and cohesive.
The sound is warm and open with a wide soundstage both left to right and front to back. The trebles are not harsh, which has been a criticism with past implementations of the Sabre 9018.
I initially fired it up with just the USB cable and it sounds great, but adding a 6V DC power supply improves the sound even more.
I shall try it with an optical cable over the next few days and with the drivers when they are available.
Going with the OPA2134 jfet chips was an excellent idea, they are my favorite op-amps outside of the Sparkos and Burson op-amps. The OPA2134 are very clean and detailed op-amps.
HiFime get's a 10/10 at the initial listening stage.