I experimented with a Naim preamp upgrade from a 72 a few years ago – really out of curiosity. It dramatically changed the sound of the system in an impressive way. But after a few months all I wanted was to return to the 72. I sold the upgrade within an hour to a chap who couldn’t believe his luck at the price and , with some difficulty, managed to buy another 72. System BALANCE was restored – there was less at the frequency extremes, which the other pre often forced me to concentrate on, and easier, relaxed, listening resulted.
The 72 just seems to get to the heart of the music and draw out the essentials.