Legendary musician's old Rush EP is warped (7)
I believe the answer is:
orpheus
'legendary musician's' is the definition.
(I've seen this before)
'old rush ep is warped' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'is warped' indicates an anagram.
'rush'+'ep'='rushep'
'rushep' is an anagram of 'rpheus'.
'o'+'rpheus'='ORPHEUS'
(Other definitions for orpheus that I've seen before include "Legendary lyre-playing poet" , "A fabulous musician" , "In Greek myth he followed his wife Eurydice into the underworld" , "One who lost his wife" , "Taj Mahal city" .)