sophie
Break My Heart
...what?
Why would you have a letter which you cannot pronounce o_O?
Like many things in English: orthography is wack, yo.
x in non-initial position: /ks/ as in ax or klaxon or execute.
x in initial position: /z/: as in xenophobic or xerox (/ˈziːɹ.ɑks/)
English phonotactics do not allow for word-initial /ks/, hence cardgame's confusion about how such a sound would be possible. The same is true for word-initial /ps/. In loan words with word-initial ps, English defaults to /s/, as in psychology: /saɪˈkɑlədʒi/. Both word initial /ps/ and /ks/ are valid in other languages like German or Ancient Greek.