Today's high-end audio has become all about mixing circuit topologies and parts to make a sonic blend that the designer thinks “sounds about right”.  You'd almost forget that getting closer to the sound as crafted by the artist really means keeping the replay system from changing it. Turning this simple insight into hardware is probably the toughest way to do audio. All simple circuits change the signal audibly, so one has to get to grips with more complicated ones that don't. I analyse every subcircuit mathematically and look for ways to eliminate every error term.