Thanks for yor reply, I realise it is not possible at the moment, I was suggesting it as a future impovement to avoid multiple remote controls, it seems a bit of an oversight to supply high quality remotes that are not very smart that may as well be left in the box.
I do not use the RoseConnect app as it is not very good, I use Qobuz Connect instead.
You can control the volume of the RS451 and RA280 through the RoseConnect app.
Please refer to the link below for more details:
However, even in the future, it seems difficult to control two silver remote controls with a single remote.