I might add that I was on 2 support calls today with sonos. The first had no idea what I was asking. The second kept saying this was an apple question. 

Yes, in the ATV ‘Settings/Video & Audio/Audio Output’ you can select any Airplay capable device that’s available on the same network subnet to output the Apple TV audio to that speaker. The volume control can be adjusted in the same screen too using the + & - on the ATV remote as this screen-capture image shows from the ATV settings screen:

Ken - Thanks for your response. I posted this question because currently we are feeding a signal via HDMI to a projector. From the projector we using the audio out (mini) to a Sonos connect (rca). The Sonos connect then wirelessly feeds 4 1st and 2nd gen Sonos 3s and 5s.

My hope is is eliminate the Connect and wirelessly connect the ATV to a pair of Sonos Fives via airplay. And if all possible is the volume from the ATV to the Sonos Five truly manageable from the ATV remote.

From your response above it seems it is. Is this correct?

If you have more than one Airplay speaker connected, then I ‘think’ you may have to go into the screen shown in my earlier post to select and change the volume of the speaker(s), but (I think) you can select an Airplay device as default and control it with the remote, but in my case the remote normally defaults to the (connected) TV volume using CEC over the HDMI port - I thinks it’s a case of trying it and see what happens.

If you have an ATV and any Airplay speaker available to you now, you can perhaps test this will work for you, before purchasing the Fives. Note anyway you can control the volume of any Airplay device using any iOS mobile device too from its Airplay list or Siri voice control and there are hardware volume controls on the Five’s too, so you have several options to adjust their volume.