I have the same issue with Zone B with not being able to control it using the integrations. I originally was using the yamaha integration the same way as the original post. But then after reading this thread changed to the yamaha_musiccast integration. It appears that i am still unable to control power of Zone B.
I can use the Yamaha AV controller app from my phone to turn on and off Zone B successfully but do not see how i can do this from home assistant.
I have a second set of speakers in my kitchen area which i want to be able to turn on via home assistant which will just play the same audio which is on the main zone. While i can do this via the yamaha app i would like to be able to control in home assistant so i can create automatons.
Here is an extract of a query to /YamahaExtendedControl/v1/system/getFeatures which contains some zone_b information.
{"response_code":0,"system":{"func_list":["wired_lan","wireless_lan","wireless_direct","network_standby","network_standby_auto","bluetooth_standby","bluetooth_tx_setting","zone_b_volume_sync","hdmi_out_1","airplay","disklavier_settings","remote_info","network_reboot"],"zone_num":2,"input_list":[{"id":"spotify","distribution_enable":true,"rename_enable":false,"account_enable":false,"play_info_type":"netusb"},
{"id":"juke","distribution_enable":true,"rename_enable":false,"account_enable":true,"play_info_type":"netusb"},
{"id":"qobuz","distribution_enable":true,"rename_enable":false,"account_enable":true,"play_info_type":"netusb"},
{"id":"tidal","distribution_enable":true,"rename_enable":false,"account_enable":true,"play_info_type":"netusb"},
{"id":"deezer","distribution_enable":true,"rename_enable":false,"account_enable":true,"play_info_type":"netusb"},
{"id":"airplay","distribution_enable":false,"rename_enable":false,"account_enable":false,"play_info_type":"netusb"},
{"id":"mc_link","distribution_enable":false,"rename_enable":true,"account_enable":false,"play_info_type":"netusb"},
{"id":"server","distribution_enable":true,"rename_enable":true,"account_enable":false,"play_info_type":"netusb"},
{"id":"net_radio","distribution_enable":true,"rename_enable":true,"account_enable":false,"play_info_type":"netusb"},
{"id":"bluetooth","distribution_enable":true,"rename_enable":false,"account_enable":false,"play_info_type":"netusb"},
{"id":"usb","distribution_enable":true,"rename_enable":true,"account_enable":false,"play_info_type":"netusb"},
{"id":"tuner","distribution_enable":true,"rename_enable":true,"account_enable":false,"play_info_type":"tuner"},
{"id":"hdmi1","distribution_enable":true,"rename_enable":true,"account_enable":false,"play_info_type":"none"},
{"id":"hdmi2","distribution_enable":true,"rename_enable":true,"account_enable":false,"play_info_type":"none"},
{"id":"hdmi3","distribution_enable":true,"rename_enable":true,"account_enable":false,"play_info_type":"none"},
{"id":"hdmi4","distribution_enable":true,"rename_enable":true,"account_enable":false,"play_info_type":"none"},
{"id":"av1","distribution_enable":true,"rename_enable":true,"account_enable":false,"play_info_type":"none"},
{"id":"av2","distribution_enable":true,"rename_enable":true,"account_enable":false,"play_info_type":"none"},
{"id":"av3","distribution_enable":true,"rename_enable":true,"account_enable":false,"play_info_type":"none"},
{"id":"audio1","distribution_enable":true,"rename_enable":true,"account_enable":false,"play_info_type":"none"},
{"id":"audio2","distribution_enable":true,"rename_enable":true,"account_enable":false,"play_info_type":"none"},
{"id":"audio3","distribution_enable":true,"rename_enable":true,"account_enable":false,"play_info_type":"none"},
{"id":"aux","distribution_enable":true,"rename_enable":true,"account_enable":false,"play_info_type":"none"}]},"zone":[{"id":"main","func_list":["power","sleep","volume","mute","sound_program","direct","enhancer","tone_control","dialogue_level","signal_info","prepare_input_change","link_control","link_audio_delay","link_audio_quality","scene","cursor","menu","surr_decoder_type","contents_display","actual_volume"],"input_list":["spotify","juke","qobuz","tidal","deezer","airplay","mc_link","server","net_radio","bluetooth","usb","tuner","hdmi1","hdmi2","hdmi3","hdmi4","av1","av2","av3","audio1","audio2","audio3","aux"],"sound_program_list":["munich","vienna","chamber","cellar_club","roxy_theatre","bottom_line","sports","action_game","roleplaying_game","music_video","standard","spectacle","sci-fi","adventure","drama","mono_movie","2ch_stereo","7ch_stereo","surr_decoder","straight"],"surr_decoder_type_list":["toggle","auto","dolby_surround","dts_neural_x","dts_neo6_cinema","dts_neo6_music"],"tone_control_mode_list":["manual"],"link_control_list":["speed","standard","stability"],"link_audio_delay_list":["audio_sync","lip_sync"],"link_audio_quality_list":["compressed","uncompressed"],"range_step":[{"id":"volume","min":0,"max":161,"step":1},{"id":"tone_control","min":-12,"max":12,"step":1},{"id":"dialogue_level","min":0,"max":3,"step":1},{"id":"actual_volume_db","min":-80.5,"max":16.5,"step":0.5},{"id":"actual_volume_numeric","min":0.0,"max":97.0,"step":0.5}], "scene_num":4,"cursor_list":["up","down","left","right","select","return"],"menu_list":["on_screen","top_menu","menu","option","display","red","green","yellow","blue"],"actual_volume_mode_list":["db","numeric"]},
{"id":"zone2","zone_b":true,"func_list":["power","volume","mute","prepare_input_change","actual_volume"],"input_list":["spotify","juke","qobuz","tidal","deezer","airplay","mc_link","server","net_radio","bluetooth","usb","tuner","hdmi1","hdmi2","hdmi3","hdmi4","av1","av2","av3","audio1","audio2","audio3","aux"],"range_step":[{"id":"volume","min":0,"max":161,"step":1},{"id":"actual_volume_db","min":-80.5,"max":16.5,"step":0.5},{"id":"actual_volume_numeric","min":0.0,"max":97.0,"step":0.5}],"actual_volume_mode_list":["db","numeric"]}],"tuner":{"func_list":["am","fm","rds"],"range_step":[{"id":"am","min":531,"max":1611,"step":9},{"id":"fm","min":87500,"max":108000,"step":50}],"preset":{"type":"common","num":40}},"netusb":{"func_list":["recent_info","play_queue","mc_playlist","streaming_service_use"],"preset":{"num":40},"recent_info":{"num":40},"play_queue":{"size":200},"mc_playlist":{"size":200,"num":5},"net_radio_type":"airable","pandora":{"sort_option_list":["recent","alphabet"]}},"distribution":{"version":2.00,"compatible_client":[2],"client_max":9,"server_zone_list":["main"]},"ccs":{"supported":true},"privacy":{"gdpr_supported":true}}