It's not "KA-hone-ays" (that means "boxes" by the way). It's not "COO-hone-ays" (which means nothing, i think, although to American ears it's eerily close to "cooties" which means germs).
It's not spelled "cajones" (that means boxes, and no there is no particular association with boxes and testicles in Spanish).
The correct pronunciation is "Ko-HONE-ays". Emphasis on the 2nd syllable. The correct spelling is "cojones".
That is all. Thank you.
ps: alternatively you can say "HWAY-bos" (spelled "huevos") which in Spanish means "eggs" but colloquially, like "balls" in English, is acknowledged as having a 2nd meaning. But God knows what English tongues would make of huevos... "HOO-vos"?