St. Cecilia is the patron saint of music, so the organ and cherub (putto) with trombone reflect that symbolism. Why Cecilia has the heads of Valeriano and Tiburtio on a platter is beyond me, but it’s too bad they didn’t get to hear the trombone and organ music.
I just added this painting and caption to the Trombone History Timeline (17th century—first half). Below the color image is the black and white reproduction that can be found at the The Digital Library of the National Library of France website. You will notice that the images are reversed.
For more images of cherubs (putti) playing trombone, see Trombone History: Cherubs Playing the Trombone.
c. 1620—Italy: Italian Baroque painter Bernardo Strozzi includes a putto holding a trombone in the painting, Santa Cecilia con le teste di Valeriano e Tiburtio (see below image; public domain) (source: The Digital Library of the National Library of France).