The (extremely) Baroque plasterwork may be by Francesco Vassalli of Lugano, known to have been active in Northern England from 1724 to 1763.
The figures around the ceiling are Roman emperors accompanied by martial decorations, whereas those on the walls are the nine Muses with symbols of the arts they inspired. The name 'Music Room' is likely to be a corruption of 'Muses Room', as it was a room from which to view the semi-formal garden rather than a music venue.