As a long term Mi 75 QLED user, I can only talk about the brilliant picture quality and the amazing brightness it offers. The power consumption is some 350W when the screen is white - that should give you an idea of the brightness produced. I've connected it to a 5.1 soundbar (Sony HT-RT3) via HDMI ARC and I have a very good experience watching HDR content with 5.1 surround. The built in speakers are decent, but the 5.1 experience is much much better.
ASS - can't comment, have not had to use
Upscaling HD content - 720p onwards is fine to watch. 480p and lower are unpleasant - the TV is simply too large and the input pixels too few to be smoothed out.