I've not tried using a float instead of a boolean to change the mute state, though others have reported success with that method. (I don't want to start a debate but 0 is an Integer - 0.0 would seem the correct syntax for a Float). If I have time in the morning I'll try it and see what syntax works on our system.
Have you tested the network connection between the Qlab computer and the Galileo? Are the IP addresses of both your Mac and the Galileo in the correct range with matched subnet masks? Using Network Utilities on the Mac, can you successfully ping the Galileo? If that is all working, try running OSC monitor on your mac to monitor port 15007 and send /ping from Qlab to the Galileo, if your connection is good the Galileo should respond with /pong. Assuming all of that is working, if your mute commands still are not functioning, perhaps you could try recalling a snapshot with the mutes in the state you are trying to achieve. /recall with a snapshot number between 1 and 999 will trigger a recall on the Galileo.