I’ve followed your directions (several times) and there was still no sound coming out when I select the max2play device. Music plays on my other devices (phones, Google Home). I deactivated the Spotify Connect plugin, reinstalled Squeezebox and Audioplayer, and the music played for a minute or so and then dropped out. I could restart the music from the phone and it seems to be okay right now. No Spotify Connect though.
Thanks for your persistence.