Rossi's madrigal output from this period is remarkably chromatic, to a level matched only by the music of such experimental composers as Carlo Gesualdo.
Rossi's first known opera dates from his second period of Roman service, while in the retinue of the wealthy Taddeo Barberini.
His opera Erminia sul Giordano was premiered during the Carnival of 1633 at the theatre of the Palazzo Barberini (Rossi himself played the violin on stage as the sun-god Apollo), and appeared in print four years later.
They are stylistically close to the music of Carlo Gesualdo and Johann Jakob Froberger, while being individual, and they enjoy a reputation as a significant milestone in the keyboard literature.
While the publication date of these toccatas is usually cited as 1657 [the year after Rossi's death], which is printed on one of the four surviving copies, it seems clear from research and deduction by Alexander Silbiger that they more likely were first published in the early 1630s, which not only fits with the characteristics of their style but also implies that the other keyboard composers such as Frescobaldi could easily have been influenced by Rossi as well as vice versa.