Satan's grand speeches in Milton's Paradise Lost are held shortly after the devils' Fall, but in Tasso's poems the episode is set in the year 1099, at the end of the First Crusade, so Satan already knows everything about the creation of Man and Man's salvation in Christ - while in PL he could only take a wild guess, and quite badly, for that matter.
In spite of this, Tasso gives his long poem/s a universal scope both with regard to space and time: in fact, virtually all the peoples of the Earth partake in the war (China and India included), and the historically limited event of the Crusade turns into a bird's eye view on the whole of human history and the history of salvation. That's why Milton can easily draw on Tasso's verses for his own Genesis-based poem.
Could a reference to Dante be missing? No! Satan's pain in recalling bliss while in hell comes from some statements by damned souls in Dante's Inferno, e.g. Canto 5: 121-122 and 24: 133-134. Farther on, this attitude could already be found in the words of the spirits in Hades according to Greek and Latin classical poets, e.g. see Aeneid 6: 514.