In order to fulfil a promise I made to young master Mike Hicks in which I said I would clarify which old Enid pieces were quoted on To wake the King, I hereby set out in plain (ish) English a list of those very pieces.
The Prelude has just a hint of the Chorale from Sanctus in it. This chorale was written by Willie and based on an English folk tune The Lowlands of Holland.
Ecchoing Green uses a different harmonisation of the same melody in the slow section.
On Merlin's Ground directly quotes the guitar riff from In the Region.
The Track of The Moon on The Water carries a reference to The Dreamer
On Secret Green harks back to Aerie Faerie Nonsense and Ondine (believe it or not)
Lady Morgana's Orrery has a hidden reference to an old and unrecorded track called The Star that was dropped from In the Region.
Camlann has the Dies Irae prominently displayed, just like Judgement from In the Region.
And of course Nimue has a quote from Fand.
There you are, that's them. I expect you got most of them, but not Secret Green and Lady M.