It would be interesting to read your opinion on the Stax 009s with a genuinely high-end source. I understand your feelings in many ways, even if I don't entirely agree. Also think you don't understand headphone efficiency if you think impedance is a measure of efficiency.
I did have a similar experience to yours where, when comparing Stax O2s with HD-600s, I preferred, in many ways, the Sennheisers, but this was due to a difference in frequency response and a less than ideal for the Stax. I haven't been through the entire thread so sorry if this has been asked before, but can I asked for more thoughts on different rigs you used the LCD-2s with? I've had very mixed results with them, from lack-luster to great.