Clue: Many an instrument playing in Llaregyb (6)
Answer: MORGAN
Explanation: Definition: playing in Llaregyb
M (1000. many) + ORGAN (instrument). Llaregyb is a bowdlerised spelling of Llareggub, the setting of Dylan Thomas's *Under Milk Wood*, which includes a character called Organ Morgan. We had the correct spelling of the town recently as an answer in an Orlando puzzle, so I don't know why Gordius has chosed this version here.