I wrote an article on modern approaches to chocolate ice cream a couple of months ago. There's an addendum with more notes, including tasting notes on some chocolate.
The goal was to convey a sense of dark chocolate (as opposed to milk chocolate), and to capture as many of the origin flavors as possible from a single-origin couverture.
TL;DR:
Chocolate ice cream is challenging, because cocoa butter is bad for texture. It's rock-hard when it's cold. You can't use lots of couverture and have good texture, no matter how many technical hoops you jump through. You can get a pretty good compromise by supplementing a moderate amount of couverture with cocoa powder.
If you could get high-quality, single-origin cocoa powder, you could achieve the best possible results. Just ditch the couverture. Unfortunately, most cocoa powder available today is just byproduct, even you're buying from Valhrona or Cluizel or Amedei. It tastes good, but it's not interesting. Who even knows what you're getting. They don't treat this stuff like their single-plantation varieties.
This seems to be changing. Some companies are starting to offer SO cocoas. Callebaut/Bensdorf has a line (but I can't get my hands on a sample). Lots of smaller chocolate companies are offering them, too, but typically are unable to mill the cocoa fine enough for smooth textures in ice cream. But my fingers are crossed that options will appear soon.
In the mean time, I make chocolate with a mix of couverture and cocoa. It's pretty great. Some of the tricks for best flavor are to eliminate eggs, keep the milk fat below 10%, keep the sweetness down, and to use sugars with maximum freezing point depression (dextrose, fructose). Total solids should be high ... 40–43%. Finally, serving temperature is important. Cocoa butter is more sensitive than milk fat to temperature. If you don't let the ice cream warm up adequately before serving, it will be slow to melt in the mouth and will have a muted flavor release, no matter how much chocolate you've crammed in there.
