You have given me food for thought here Connlyn and I thank you.
Critic Jeff Rider comments, "What makes Sir Orfeo so remarkable is the degree of critical response it has generated, the high praise it has earned, and the almost utter lack of accord among critics as to its interpretation. The poem seems to be remythified with each reading; each reading makes us feel that the previous one, even yesterday's, was inadequate."
Apart from the obvious missing elements of the looking back by Orpheus and the loss of Eurydice in the 'original' myth I personally think that the story of Odysseus and his ten-year journey home which involved being kept under the spell of a witch (Circe), his recognition by a shepherd and his cunning ploy to regain his Kingdom are other Greek epic elements in the tale of Sir Orfeo.