F1 sounds great with the K1000s, and even better with the Cicadas. I'm using the Moth EC2a3 to drive the K1Ks primarily, now, owing to that fact.
I'd love to have the chance to run the F1 against another 10 watt Pass amp of a more conventional design like the F3 and see if The F1 is so brilliant because of the unorthodox design, or despite it. It seems that many here with a much more thorough knowledge of circuits than myself already have their position on the issue, but my talents lie elsewhere, so I'd have to plug them in.