The sound field settings are not available while using Chromecast built-in (STR-DN1070, STR-DN1060, STR-DN860).

With the firmware update on 04/18/2017, 2ch or Multi can be selected when using Chromecast built-in (previous name: Google Cast) function.  
Please select the sound field as follows.

• For STR-DN1060/STR-DN860
• 1. Select AMP MENU on the remote control.
  2. Select AUDIO.
  3. Select CAST SOUND.
  4. Select 2CH or MULTI.
  5. 
     
• For STR-DN1070
• 1. Press 2CH/MULTI on the remote control.
  2. Select  2CH STEREO or MULTI CH STEREO.