Simplify the following text for a Grade 11 native English-speaking person.
Original: MacMillan gave lectures on each of the nine symphonies of Beethoven which were followed by a performance of the symphony in piano duet arrangement played by MacMillan and Dale .
Simplified: Ernest MacMillan gave lectures about each of the nine symphonies by Beethoven , after which he and Dale would play the whole symphony in a piano duet arrangement .