Fred, I assume that your other thread on the Bach disc was based on all the speakers playing, not just the sub. I've suggested a few times that to see how "quick", "tight", "musical", etc. a sub is by itself that the speakers be disconnected while retaining an 80Hz or lower crossover in the receiver. Those qualities are almost entirely due to upper harmonics of a fundamental tone played by the sub, and those harmonics are played by the speakers. The very low bass fundamental actually played by the sub itself is "muffled/subdued" as you observed, and not very "musical".
To some extent the level is also lower, since the sound power in the harmonics is absent. The sub frequencies aren't necessarily "power hungry" as we sometimes see stated, since frequency isn't determinative of power requirements; level alone determines that. For example: 50Hz, 500Hz or 5000Hz at the same level uses the same amount of power and a 90dB 500Hz note requires 10 times the power that a 80dB 50 Hz note does.
