I suspect that it could be the reverse, that Vox is an English language spelling of Wachs. The latter name literally means "wax" and is probably a metonymic for a candle-moulder (chandler) or a dealer in wax. If you know any German you can garner more from this page -
http://www.familie-greve.de/modules.php?op=modload&name=lexikon&file=index&id=1&val=w
If not a reworking of Wachs, Vox may be connected to the Dutch and Low German Vos and Voss, which mean "fox".