Bombay, I have one minor quibble with your post - passive elements CAN lower the noise floor by reducing the bandwidth of the power line noise. RMS noise is proportional to the square root of the bandwidth. However, the filters used in this approach usually degrade the transient response of the system. Active regeneration can lower the noise floor and still provide good transient response, constrained only by the dynamic current delivery capability of the regenerator's output.
Listening Fatigue
What do you guys think contributes more to listening fatigue. Volume, or the type of electronics or speaker you have? thanks