I'm not sure we really try to create a "sound signature" at all. From my perspective, we simply try to make something as transparent as possible. Usually we do some blind listening tests between 2-4 options and have to select which one we like better without knowing what parts or design is in each option. So, it's mostly sorting through designs and parts that Joe puts together based on purely technical issues.
Now, that doesn't mean I think we have an 'objective' process because it is forwarded by the subjective opinions of a number of people, but it is not a process where we're looking for a particular 'signature sound' either---though we might end up with one as it's mostly the same subjects doing the testing.
As to your fundimental question of do we 'burn in' stuff before doing the testing. Um, I guess we don't intentionally, though some gear will be burned-in. For the most part I believe burn in is a fairly small effect on electronics gear. Headphones seem to need more of it, in my opinion, but it's still a pretty small effect with a few exceptions. (The 701 needs a lot of it IMHO, for example.) I think we hear the basic differences of electronics without spending a lot of time burning them in.
