How to use a preferment / poolish? Cake vs ADY?
On the preferment: I have never seen the yeast in it included in the calculation. See it as "just another ingredient" and calculate the rest just as you would if it hadn't been there. For example, Reinhart's formula for poolish ciabatta is: 


  poolish: 169%, bread flour: 100%, salt: 3.3%, instant yeast: 1.3%, water: 33%. 


It doesn't eliminate the need for yeast at all. But as you see from this recipe, you will mess up the hydration if you try to add poolish on top. You can try recalculating it based on what hydration you already have in the preferment, but you won't end up with the same texture as the same hydration without the poolish, because it behaves a bit differently. So it will be easier to not manipulate recipes, but to choose another recipe which includes a preferment from the beginning. 

On the question of taste: if you want the yeasty aroma you smell in cake yeast, you shouldn't be using any preferments at all. This kind of aroma is what you get from an overactive yeast colony, and for that you have to use high amounts of yeast (about 8-10% cake yeast or 3-4% dry yeast) with a very quick and warm rise, ideally around 35 C. Proof for 1-2 hours only, but pay attention to not overproof. It doesn't matter if you start with cake or dry yeast here, it's about the conditions in which the yeast grows. The preferment does the opposite of that.