The impedance I get -- every Lowther driver I know is is a nominal 8 ohms, which is a far cry from the K1000s 120 ohms. Sensitivity I'm unsure of, since I'm not certain how to adjust the K1000s stated sensitivity of 74 d/mW into a more standard dB/1 watt at 1 meter sensitivity rating. The lowthers (and, to a lesser degree, the Fostex) all hover in the neighborhood of 100 dB/w.
I definitely see what you're getting at, Marc, and I get that the F1 is an immensely esoteric amplifier. Nonetheless, I'm excited to give it a go-round on my K1000s