In Stephen Baxter's Xeelee universe there is a race called the Qax who conquered humanity and enslaved them for three hundred years, starting around 5088 AD. As I've read the stories I've mentally pronounced "Qax" as "quacks" probably because it is a mildly amusing tag to apply to ruthless dictators. But I don't remember reading how Qax was supposed to be pronounced.
... These numbers had been assigned by the long-vanquished Qax - pronounced 'Kh-axe', the alien occupiers of Earth in the years before Hama Druz. The huddling domes of the Conurbations, bubbles of blown rock, were essentially Qax designs; they had been preserved as a kind of permanent memorial of that dreadful time. But Nilis, with a wink, told them that the locals referred to their cities by much older, pre-Occupation names, though not a trace of those older settlements had survived the time of the Qax. Thus they had first landed at Berr-linn, and Nilis's base was in a city called Lunn-dinn.