I've owned the Boulder 866 with the onboard digital for about five months or so and just love it. I'll cut to the chase with my appraisal: it is the most correct and complete presentation of music that I've ever had in my room. For the relatively small difference in cost, getting the analog + digital version is a no brainer.
I had a Devialet for about a year and thought it sounded clean, dynamic, and quiet but it was ultimately not as musical or involving as the tube gear I was used to, so I moved on. The Boulder is another story entirely, at least in my system. The only way I can think to describe it is also pretty boring--it is just about dead neutral, neither over nor under emphasizing any particular aspect of the sonic picture. Don't get me wrong. The Boulder is anything but boring. In fact, it checks all of my boxes, has plenty of power, and is the first solid state unit I have owned that did not have me pining for tubes within a couple of months. I guess I've always felt that tubes have that "breath of life" that solid state just can't do, but the Boulder 866 is definitely alive. It is dynamic and resolving, but also has texture and a holographic soundstage, though not artificially so. I can and do listen to it for hours without a hint of fatigue, and it excels with all kinds of music, which is crucial for me.
I have heard some Pass Lab mono blocks at length at a friend's house and was suitably impressed, but I would be hesitant to draw much of a conclusion without a head-to-head comparison in my room and in the context of my own system. I have always been intrigued by darTZeel gear, but once I was able to audition the Boulder, I knew my search was over. When I listen to the 866, there is no nagging sense that something is missing or just a bit off. It just sounds right to me.
I am able to stream Amazon Music HD and Qobuz from my iPad, so I wouldn't think you would have any issues there, though I am unfamiliar with your source and would obviously defer to a dealer on that question.
If you can get an in-home audition, do it. Yes, it is "really damn good."