The hellish hound is Cerberus, guardian of hell-gates. The Orphic lyre is a conventional symbol of poetic power. When Mercury killed him, Juno placed his eyes in the peacock's tail. The metaphor is from the strings of the lyre, which, strongly plucked, would become slacker in tension and produce notes of a lower pitch. The Romish Tityrus is Virgil, who was favoured by the emperor Augustus Caesar and whose patron was Maecenas.
Wine is an aid to poetic inspiration.
The ivy was sacred to Bacchus. He would be able to write tragedy.