Although all his recordings are in mono, he's the best of best, a pure and true artist. As some musicians from Berliner Philharmoniker who experienced both Furtwängler and Karajan said, Karajan is a great saleman who sells music great, but Furtwangler is just a genis artist who brings music out of us.
Can't find any long recording of Bayreuth Festival in 1951 online, and I encourage you to buy this CD. Beethoven's 9th Symphony is the highlight of all symphonies in history, and Furtwängler's interpretation and conducting art is simply the best of all time. No one conducts the 9th as he did. Einfach zauberhaft und unvergis*****ar!
Performance at Hitler's birthday in 1942
Performance in Salzburg in 1951