sonos_connect_sync.yaml

blueprint:
  name: Sonos Connect Sync
  description: Sync volume and source control between Sonos Connect and the receiver it's connected to.
  domain: automation
  source_url: https://gist.github.com/Qonstrukt/ca1e761b2ec0a2d52fdb8c86490fbcbd
  input:
    sonos_connect:
      name: Sonos
      selector:
        entity:
          integration: sonos
          domain: media_player
    receiver:
      name: Receiver
      selector:
        entity:
          domain: media_player
    receiver_source:
      name: Receiver source name
      description: The source name of the receiver associated with your Sonos.
      default: Sonos
      selector:
        text:
    turn_off_delay:
      name: Receiver turn off delay
      description: Delay before the receiver will turn off after Sonos stopped playing.
      default: 300
      selector:
        number:
          min: 0
          max: 3600
          unit_of_measurement: seconds
    sync_volume:
      name: Synchronise volume
      description: Synchronise volume between Sonos and Receiver.
      default: true
      selector:
        boolean:
    sync_volume_buffer_time:
      name: Buffer time between sync
      description: Time to wait before synchronizing the volume between devices.
      default: 1000
      selector:
        number:
          min: 500
          max: 3000
          unit_of_measurement: milliseconds

mode: queued

variables:
  receiver_entity: !input receiver
  receiver_target_source: !input receiver_source
  receiver_current_source: >
    {{ state_attr(receiver_entity, 'source') }}
  receiver_current_volume: >
    {{ state_attr(receiver_entity, 'volume_level')|float(0) }}
  sonos_entity: !input sonos_connect
  sonos_current_volume: >
    {{ state_attr(sonos_entity, 'volume_level')|float(0) }}
  sync_volume: !input sync_volume

trigger:
  - platform: state
    entity_id: !input sonos_connect
    to: playing
    id: sonos_playing

  - platform: state
    entity_id: !input sonos_connect
    from: playing
    for:
      seconds: !input turn_off_delay
    id: sonos_paused

  - platform: state
    entity_id: !input receiver
    attribute: source
    from: !input receiver_source 
    id: receiver_source_changed

  - platform: state
    entity_id: !input sonos_connect
    attribute: volume_level
    for:
      milliseconds: !input sync_volume_buffer_time
    id: sonos_volume

  - platform: state
    entity_id: !input receiver
    attribute: volume_level
    for:
      milliseconds: !input sync_volume_buffer_time
    id: receiver_volume

action:
  - choose:
    - alias: "Switch receiver source"
      conditions:
        - condition: template
          value_template: >
            {{ trigger.id == "sonos_playing" }}
        - condition: template
          value_template: >
            {{ receiver_current_source != receiver_target_source }}
      sequence:
        - service: media_player.select_source
          entity_id: !input receiver
          data:
            source: !input receiver_source
        - delay:
            milliseconds: !input sync_volume_buffer_time
        - service: media_player.volume_set
          entity_id: !input receiver
          data:
            volume_level: >
              {{ sonos_current_volume }}

    - alias: "Turn off receiver"
      conditions:
        - condition: template
          value_template: >
            {{ trigger.id == "sonos_paused" }}
        - condition: template
          value_template: >
            {{ receiver_current_source == receiver_target_source }}
      sequence:
        - service: media_player.turn_off
          entity_id: !input receiver

    - alias: "Switch Sonos playing state"
      conditions:
        - condition: template
          value_template: >
            {{ trigger.id == "receiver_source_changed" }}
      sequence:
        - service: media_player.media_pause
          entity_id: !input sonos_connect

    - alias: "Change receiver volume"
      conditions:
        - condition: template
          value_template: >
            {{ trigger.id == "sonos_volume" }}
        - condition: template
          value_template: >
            {{ sync_volume }}
        - condition: template
          value_template: >
            {{ receiver_current_source == receiver_target_source }}
        - condition: template
          value_template: >
            {{ trigger.to_state.attributes["volume_level"] != receiver_current_volume }}
      sequence:
        - service: media_player.volume_set
          entity_id: !input receiver
          data:
            volume_level: >
              {{ trigger.to_state.attributes["volume_level"] }}

    - alias: "Change Sonos volume"
      conditions:
        - condition: template
          value_template: >
            {{ trigger.id == "receiver_volume" }}
        - condition: template
          value_template: >
            {{ sync_volume }}
        - condition: template
          value_template: >
            {{ receiver_current_source == receiver_target_source }}
        - condition: template
          value_template: >
            {{ trigger.to_state.attributes["volume_level"] != sonos_current_volume }}
      sequence:
        - service: media_player.volume_set
          entity_id: !input sonos_connect
          data:
            volume_level: >
              {{ trigger.to_state.attributes["volume_level"] }}

Any way to eliminate delay and work with receiver that has volume limit set? For example if volume limit on the receiver is 80 you could manually set in blueprint than place volume on sonos into passthrough for smoother sync. Current problem is that sonos will always go to 100 and receiver may not making the last 20% a dead zone. perhaps 50% of sonos volume can equate to 40% of receiver if limit set to 80 in blueprint