I think I've managed to install the new version; BandLab Assistant is still saying an update is available.
My confusing experience so far:
- I opened BandLab Assistant and it said a new version was available (of itself) so I clicked to update.
- This took a couple of minutes but it was an anxious wait as nothing showed on the screen that anything was happening. But it was so all ok.
- The Assistant then said a new update was available for CbB so I clicked for it and it said 'installing' for seven or eight minutes, then finished, although no signs of installation appeared on the screen.
- I opened CbB and checked the version number: no change, still the old one.
- I clicked install again on the Assistant and a few minutes later all the expected popups appeared unpacking and installing the new files.
- I was then asked if I wanted to install Studio Instruments and clicked 'no'.
- I opened CbB and all seems well, including the Powr dithering options reappearing (thanks guys!)
- But: the Assistant is still saying 'a new version is available'.

Puzzled.
EDIT: I installed again and got to the same problem. I guess if I don't want Studio Instruments I will always have to put up with the Assistant telling me I need a new version. Bring back the Command Centre which understood me!