Jag-U-Wire
Aww, come on . . . After years, now, of Steve Jobs' mostly-dealing-with-OSX Keynote addresses streamed live into packed Apple Store theaters, then on the Apple website, fans hanging on every word he utters on stage in front of a two-storey-high OSX graphic, AND NONE OF YOU MACHEADS REMEMBER HOW STEVE PRONOUNCES "OSX" ???!?!? (That would count as official . . .)
Oh, wait; This is the guy who pronounces Jaguar "Jag-You-Wire"!
Nevermind.
(I think either way sounds great; when I want to feel wild, free, cool and creative, I say "O S eX" [as in "EXtreme"], but when talking to a tech administrator & wanting to sound buttoned-down professional, I say "O S Ten" . . !!)