The way Jerry tapped his Fender preamp is, like you said, a fairly high output impedance. No buffering or impedance matching was used. The Alembic F2B is the same situation. However, Jerry's McIntosh input impedance is quite high at 250kOhms, so the match there is ideal.
Not sure exactly why you'd suggest that a high Z output would have a loss of highs. Maybe because it could be more vulnerable to cable capacitance, but with reasonably short runs of under 10' of cable, preferable 3' or so, there doesn't seem to be any effect on the audible band (up to 20kHz or so).
The one thing I alter in the SMS Classic is to take that output tube and utilize both halves of it by running the two triode sections in parallel. This effectively cuts the output impedance in half giving DOUBLE the drive capability and without changing the tone at all. Some people would suggest using a very low-Z cathode follower at the output to really have drive capability into any kind of load. But in practice, the parallel triode seems to be fine into any amp input load I've found. And really, even the single triode driving the output like Jerry's output from a Fender really seems just fine into the many load types people seem to try.