He can use the TV remote only if the Amp is set up as surround speakers connected to the Arc. If the Amp is set up as a separate room, the only way to control that ‘room’ is either via the controller app, or the button controls on the Amp itself. 

Ok thank you! I figured I was missing something. 
 

if they are set up as the surround he would essentially only have 1 room on the app? 

Correct, just one room. Your client could potentially change the settings for that one room to stream using ‘Full’ rather than ‘Ambient’ for the surround settings, and get that pair of speaker to act as a normal stereo pair when streaming music, rather than merely supporting the Arc, but there isn’t a way to fully quiet the Arc while streaming. Of course, when playing the TV’s input, they’ll be normal surround speakers. 

Awesome! Thank you for your help. I don’t mess around with AV a whole lot. So figured I was overthinking it or missing something 

does the arc sound bar has Bluetooth connection 

No. 

I have the same situation. If I connect an Amp to an Arc as surround speakers, will there be a delay in the audio coming from the amp and the in ceiling speakers? Can I connect an Amp to a Beam and accomplish the same thing?

If the Amp is set up as a surround speaker driving device, no. If the Amp is set up as another Sonos ‘room’ from the Arc, there will be a 75 Ms delay only when using the Arc’s TV (HDMI-ARC) input, but not when streaming music to both rooms. 

This is the same situation with any Sonos soundbar. It is a function of the software, so that things can play in sync across a standard set of speakers in extra ‘rooms’.