Schumann: Piano Quintet, Brahms: Horn Trio
Serkin, Budapest String Quartet, Tree, Bloom (Vinyl)

A recording made at the Marlboro Music Festival, there's no real way of telling if this was a performance captured at the end of a series of rehearsals, or an impromptu middle-of-the-night session brought on by a moment of inspiration and heavy drinking.

It's a great recording of (in my opinion) one of the best piano quintets.
I'm not sure I understand the logic behind the canonized ensemble of the horn trio, but it is (nonetheless) some beautiful music.