How about Darker = more analytical/sterile with very sharp transients and less decay vs Warmer = more forgiving of bad a recording/musical or lush sound. One would most likely want to end up in the middle where there is a balance that sounds more like what it would if the performer(s) where live.
As far as the voltage measurements that Klaus requests when voicing them, I believe he uses a AC variable output transformer to set the output voltage, that feed the amp, to the average of what you supply him when he performs the biasing. He also adjusts the bias based on his experience of what your speakers sound like. Klaus, please correct me if I'm wrong here!
