@JAMES N, MIKE-B: thanks!
@ARDBEG10Y: the Digital Concert Hall sound is good (they broadcast with 256KBit/s, I think), the video quality is HD, I believe. Upscaling to 4K works fine. Sony has opted for Android TV. Android TV 5.1 was miserable on Sony devices but 6.0.1 is almost usable. Perhaps it is just that the MT5891 is faster than the MT5890. The KD-43XD8305 is far from ideal and I would have preferred buying a smaller device with a 10 bit panel. I have waited until last week in the hope that Apple would announce a display with integrated GPU. As this did not happen, I bought the Sony. For 900 EUR it's an honest device, I think. I hope that next year we wil have small OLED panels with 10 bits and flexible mount options.
The Digital Concert Hall app has so far been working flawlessly. I have listened to both live concerts (on Friday evening) and to concerts from the archive. I have the impression that the video quality is slightly better as compared to the video quality of the (Opera) web browser. Still, the app could be improved in different ways. For instance, I would like to be able to browse my favourites according to arbitrary tags and be able to get a list of my favourites violin concertos by, say, Isabelle Faust in the same way as I do with MinimServer. That should not be too difficult to implement.
The Opera browser is very primitive and searching and navigating without a connected keyboard and a mouse is a pain. From this perspective, Android TV is far behind Web OS. Streaming from the Wiener Staatsoper works fine but there is a nasty problem with theoperaplatform: when the cursor is not on a control widget, the control bar starts to flicker instead of disappearing. This is extremely annoying. I have not tried the browser extensively and I haven't tried to install Chrome on the TV.
