either bind the server announcements audio device to the voice audio device. or...
allow a device to be selected for server announcements.

issue causing suggestion:

teamspeak3 primary device is chsen as USB headset.
result: all voice chat comes through headset.

system defualt audio device is changed throughout day from USBheadset, back and forth with a SB X-FI(speakers)
result:
1: when headset is defualt OS audio device, all server announcements and voice come through
headset.
2: when Defualt OS audio device is changed to SB X-fi(speakers) voice chat continues to come through USB headset(as it should), but server announcements come through Speakers..........

I am using the text to speech pack. a work around is to go into control panel and change the OS voice to text device to USB. But that solution is broken once the OS device is changed to speakers again....