Here are some suggestions from David for recordings if you want to listen to any of these works before the talks. You may be able to find these on YouTube.
Verdi: look for Robert Shaw’s recording with the Atlanta Symphony. There are YouTube videos of a couple of different performances conducted by Von Karajan. There is an especially good one with a youthful Pavarotti as the tenor soloist!
Mozart: Here, the main thing is to find one that uses Sussmayer’s completion. I suggest Neville Marriner’s recording.
Brahms: Robert Shaw (he recorded it twice; both are wonderful) or Otto Klemperer. While I don’t love the soprano on Klemperer’s recording, he brings out some wonderful details in the score. The baritone is Fischer-Dieskau at his best.