The Grand series vs Classic series update is all but a clean sheet redesign. Only the basic aesthetics and core design remains similar.
For Haydn specifically, and Grand series generally:
Slightly larger cabinet with thicker front and rear baffles, to support new drivers and port system
Unique front port system, located behind the tweeter, for easier room placement and quieter port operation
Improved polymer blend for mid-bass driver (X3P), for more resolved, higher band-width midrange and bass frequencies
Refined tweeter design for smoother more extended high frequencies
Linear crossover layout featuring VERY high tolerance components (including .7% tolerance hand-wound inductor coils) for more efficient transmission of amp power
Custom gold-silver alloy binding posts for greater mechanical/electrical connection to speaker cables
Overall, the new Haydn Grand is more resolved, more extended on both extremes, and smoother. A commendable upgrade from an already great design!