I've actually had mixed results with the isolated amino nutritional supplements I've tried. Lysene will give a really strong toasted bread, then later almond flavor/aroma, that's interesting, but not exactly what I'm going for.
I'm pretty sure the dark fruit flavors are more of a caramelization flavor, and I think the burnt sugar is more of a caramelization flavor, although you can get the toasty/nutty/chocolatey flavors from much lower temperatures.
The problem I think is that a lot of the target compounds have a lot of intermediate stages that require precursors. So the exact mix of amino acids plays a big role in the results.
To paraphrase Dr. England - "Off-flavors smooth with time. So do mountains. Brew it right from the start!"
My blogsite: http://nateobrew.blogspot.com/