Thank you all for your thoughtful replies.

I also have available to me the following two Sony remotes:

Remote Commander RM-AV3000 and RM-P700E.

Can you advise whether one or the other of these might be to control my Home theatre System model STR-K670P (which is the receiver part of Sony HT-DDW670) and Sony Surround System DAV-FX500.

Thanks!