extracting banana flavour for an iced coffee
Consider making a banana consomme via gelatin filtration. As described in Harold McGee's 2007 NYT article, this technique produces liquids with the taste of all sorts of foodstuffs that are otherwise full of texture and color. A tomato consomme, for example, is clear and watery, rather than red and pulpy, while retaining the flavor of a tomato juice. The same technique can be (and has been) done with breads, meats, vegetables, fish, etc.

The process is to make a loose banana gel by mixing a banana with water, adding gelatin, and heating until the gelatin is dissolved. The mixture is then frozen until solid, then suspended in a strainer over a bowl in the refrigerator for a couple of days until the liquid essence distills out and the solids are left in the strainer trapped in a gelatin net.

The particular advantage I believe gelatin filtration will give you in this case is that it will give your coffee a full banana flavor without making it thick, pulpy, or cloudy.