I´ve got the WiFi-Multiroom Speaker GGMM M3 which is said to be compatible with Spotify. Unfortunately, it does neither show up in the Spotify app for android nor in the desktop version. What can be wrong there?
I don't know if you have figured this out yet but there is a firmware update available for the M3 through the Mobile App that seems to add Spotify Connect functionality. Otherwise it seems to work purely as an AirPlay speaker.