square root of 2: It’s B’feirush in Shulchan Aruch (maybe it’s a Mishnah Berurah) that if it’s to help one concentrate on Tefillah (because he would be hungry), it’s Muttar. I’m no Rav, but I would assume the Chazzan case is the same. Ayein Sham, Orach Chaim Siman 90 or so.
MA: You are completely wrong. Coffee is Muttar (according to most, not all) because it’s normal to drink coffee as part of a waking-up routine and it isn’t considered rude to HKBH to do before Davening. Other (non-water) drinks are not permitted before Davening. In fact, the Mishnah Berurah thinks it’s Assur to even put milk in pre-Davening coffee, though most Poskim nowadays think it’s okay because so few people take their coffee black.