I don't know exactly how much honey or sugar you should use. I make pizzas all the time and get sufficient browning to my taste, without adding any "browning agents." However, different recipes may react differently, and you may prefer a dough that browns faster or darker than mine.
In any case, you'll need a lot more honey or sugar to replace the diastatic malt by weight. Diastatic malt means that it has active enzymes which break down some of the starch in flour and thereby release natural sugars in the dough. Those sugars help to feed the yeast (and thus tend to cause a greater rise), but also will aid in surface browning reactions.
If you substitute diastatic malt with sugar itself, you're not trying to replace the malt powder or malt syrup -- you need to replace the sugars that the enzymes would have released into the dough. Thus, there's no possible proportion to give you: the amount of sugar released by using diastatic malt will vary depending on fermentation conditions, type of flour, and probably other factors. Again, I don't really know how to give you an exact amount of sugar/honey to use -- there are all sorts of recipes for pizza with greatly varying amounts of sugars in them. You might start by adding a tablespoon or so of sugar/honey to your dough and see what happens. (Definitely try more than 9 grams.) Adjust up or down until you get the effect you like the best. (Adding sugar to pizza dough won't just affect browning: it will alter texture and flavor too, so it's best to experiment. And note that some of the sugar will also be digested by the yeast in long fermentations, so you may need to make further adjustments depending on your procedure.)
Additionally, you might find that longer fermentation will allow natural enzymes in the dough to break down some of the sugars too and promote browning. There's a limit to this process, and you already mention a day-long fermentation in the fridge. But fermenting for 2-3 days in the fridge and/or allowing a little more time at room temperature when the dough is "warming up" for fermentation may allow the enzymes to simulate a bit of your diastatic malt effects.