[wrxtasy]

That's a tad more expensive than I was hoping for, but I'll check it out. Is it 100% confirmed that it can decode DTS-HD and Dolby TrueHD losslessly to multi-channel PCM?

It's 100% confirmed because that is what I get with my Yamaha AVR using an ATV 4K and the MrMC App.

I don't necessarily mind manually changing output resolution if it doesn't require too many button presses; but I doubt that its upscaling is as good as my Lumagen RadiancePro video processor, so the ability to output 1080p at native resolution is important.

I doubt it as good either but this is a $100-$150 media player we are talking about here.

The Vero 4K (I think) uses an S905X chipset; does the 4K+ use the same chip?

Yes I believe it is (might be a S905D), but you need Gigabit ethernet that the Vero 4K+ has for reliable 4K HDR streaming.

If so, does it have to dither 10-bit colour to 8 bits for HDR (as mentioned in the "4K HDR State of Play" thread)?

That is currently up for debate I believe. @Sam Nazarko will have more info I believe.

And am I right that it can handle 16-bit audio but not 24-bit, and downsamples higher audio bit-rates to 48kHz?

See 24-bit LPCM confirmation in THIS thread (click)
AMLogic LE Kodi will also do the same due to the shared open source Kodi code and Kernel.

What would you say are the relative merits of Vero4K+ running OSMC vs Minix U9 running LibreELEC (in playback terms)?

Very little, the MINIX U9 - S912 chipset has a few more CPU ponies for CPU software decoding of stuff like Hi10P Anime.

Currently it's faster skipping about during video playback due to the Gigabit Ethernet port, which the Vero 4K+ is now getting.
The U9 Mini Keyboard remote I find handy for Kodi Keyboard shortcuts after long term Kodi usage.

I do like the Power OFF / ON remote control ability of the U9, which then turns OFF / ON my HDMI CEC connected AVR / TV. Pretty handy, day to day.

Vero 4K+ will get continual support, past Kodi v18 Leia. Unless there is a miracle the S912 chipset will not due to Hybrid GPU drivers currently used to draw the Kodi user interface.

"Flawless" is a very exact word, and nothing is 100% perfect

That's rather depressing. Is decoding x264 and x265 video correctly really that complicated?

Realise everyone is still bug busting SDR / 4K HDR auto chroma, bit depth switching to try and make it near Flawless. There are No issues with H264 or H265 decoding I know of.

As I said, this isn't a high priority, but is there any prospect of any of these devices handling frame-packed 3D? If the answer is no, I can live with that but it might serve as a "tie-breaker" if there is.

See the Zidoo X9S thread for working 1080p 3D and then have fun dealing with a tablet Android OS.

1080p 3D ISO support may come to the AMLogic OSMC / LE devices, but it's pretty low priority. Plus lack of developers having 3D TV's these days does not help.