Well, from what i looked at cssdk (and wasn't very deep because i hadn't much time), when a client uses voice cmd, it gets gamerules and banlist to know who can hear and who can not hear. I am not sure in wich of them loopback is on. I guess gamerules is only about sv_alltalk and teams. BanList is the mute list, and i guess loopback is something to mute yourself. Yet i am not sure about this. I will look deeper tonight.