Re: the Impedance mismatch:
Looking at the circuit on my Issue#3 board (below):
The output is fed via R12 + R13 in parallel, which equals 240ohm [2400] +110ohm [1100] = 75.429ohm
The signal is then fed into a 1:1 impedance-match transformer, which provides a conjugate-match of the transmission line.
While this may not alleviate all the concerns re: Impedance-mismatch, I believe it does help to clarify the design slightly.
- I can only conjecture that the 50-ohm impedance number that Musical Fidelity quote is likely for the shunt-impedance value of the matching-transformer itself, and not the actual source impedance.