Worthy of note… Default volume settings on your Arcam use the same IR codes as Naim stereo amps.
If your Nait 3 isn’t the R (remote control) then no issue…
But if it is an R, the Naim volume will change when the Arcam changes… and as they both go up and down together the effect on the nait will be exponential and a huge problem
So you’ll need to go into the avr550 manual to customise the remote (unlock the AMP mode), access the advanced settings menu, change the IR code to system 19 (16 is standard), and change the arcam remote to the alternate or codeset.
Any Naim dealer with experience of Arcam AV will probably be able to assist, or Arcam tech support if you get stuck.