I am happily using Spotify Connect to steam audio to my HEOS speakers (from both the IOS and OSX apps). The only thing that bothers me is that the volume step level in your applications is configured to take *too big* steps when changing the volume up or down.
Please change volume step level to take smaller steps when changing the volume up or down. Refer to paragraphs 4.2.8 and 4.2.9 of the CLI protocol specification attached to message for further information.
Don't hesitate to contact me in case this needs further explanation.