I was wondering, since we pronounce the letter 'x' (chi?) with a hard c sound in XPISTOS, why not also in the word "Orthodox" or 'Maximos?"
As Heorhij points out, "X" in Greek is more of a back-of-the-throat H sound (in-between a normal H and clearing your throat there is a point where this "X" - pronounced Hee - comes from), versus the x (ex) in english which is more of a "ks" sound and has a different letter in the Greek alphabet (the "ksi" which he demonstrates in his post above).
"O Cross of Christ, all-holy, thrice-blessed, and life-giving, instrument of the mystical rites of Zion, the holy Altar for the service of our Great Archpriest, the blessing - the weapon - the strength of priests, our pride, our consolation, the light in our hearts, our mind, and our steps"
Met. Meletios of Nikopolis & Preveza, from his ordination.