Yes, it is possible to play Ultra HD on a Five.

If you let the song play for a minute or two, the stream should automatically calibrate to Ultra HD.

However, if you are using an older generation sub with the Five, then the stream is restricted to HD due to a known and as yet unresolved bug.

Also, if you are grouping any other speakers with the Five that are not compatible with Ultra HD (ie. Play:1) then again the stream will be limited to HD.

That's excellent, I'll check. Many thanks!

Precisely what happened, it takes a couple of minutes to show HD, then a couple more for Ultra HD. Many thanks for your answer!!!

Once you have Ultra HD, the stream will generally stay at that (assuming the track playing is UHD) during the listening session, rather than calibrating for every new track.

Imagine the software will improve in time to calibrate quicker as still relatively new.