Via these links you can view a number of music exhibits online.
Several other exhibits can be found in the members-only-section.
“Schubert” 
“European Opera Worksfrom Claudio Monteverdi to Richard Strauss”
Peter Plüghan / Germany
Current Owner: Auction House Christoph Gärtner
“The Evolution of Puppetry” 
“The Best Composers of Europe” 
“Foreign arists in Bohemia and Moravia” 
“In the footsteps of Richard Wagner” 
“The Barrel Organ” 
“Beethoven on Postage Stamps” 
“Tango !” 
“Maria Callas” 
“Radio for Everybody” 
“Drums” 
“Wolfgang Amadeus Mozart – His Life and his Work” 
“The History of Musical Notation” 
“Engelbert Humperdinck – A philatelic Journey through the Composer’s Life” (Single Frame Collection)Peter Lang / Germany
“El Teatro Lirico Europeo” 
“Haywood Music Collection Finding Guide” (Smithsonian National Postal Museum)
The collection is a broad compilation of thematically organized stamps, covers, commemorative sheets, and more philatelic objects. Dr. Charles Haywood donated this collection in 1984. It then consisted of 16 albums with 5,168 objects. You can download the finding guide from the museum’s homepage.
“Heifetz Music Collection Finding Guide” (Smithsonian National Postal Museum)
In 1978 the Russian-born violinist Jascha Heifetz donated his music stamp collection the museum. The five albums of this collection contain 6421 philatelic objects from around the world. The index of the collection can be downloaded from the museum’s website.