Modern musician's back, turning up with two pianos included (6)
I believe the answer is:
rapper
'modern musician's' is the definition.
(I've seen this before)
'back turning up with two pianos included' is the wordplay.
'back' becomes 'rear' ('rear' can be a synonym of 'back').
'turning up' says the letters should be written in reverse.
'with two pianos' becomes 'pp' (I can't justify this - if you can you should give a lot more credence to this answer).
'included' means one lot of letters goes inside another.
'rear' written backwards gives 'raer'.
'raer' enclosing 'pp' is 'RAPPER'.
(Other definitions for rapper that I've seen before include "Drake maybe" , "Rhyming singer" , "is making a hit?" , "entertainer who recites to rock music" , "Singer, sounds like covering" .)