initial_orientation =  1.00000,    0.00000,    0.00000
initial_rotation    = -1.39626,   -4.71239,    0.00000

new_rotation = -1.94626,   -4.71239,    0.00000

'initial_rotation' - 'new_rotation' = 'rotation_difference'

initial_rotation    = -1.39626,   -4.71239,    0.00000
new_rotation        = -1.94314,   -4.71239,    0.00000

rotation_difference = -0.54687,    0.00000,    0.00000

rotation_matrix = SharpDX.Matrix.RotationYawPitchRoll(rotation_difference.Y, rotation_difference.X, rotation_difference.Z);

rotation_matrix = 1.00000,    0.00000,    0.00000,    0.00000
                  0.00000,    0.85415,   -0.52002,    0.00000
                  0.00000,    0.52002,    0.85415,    0.00000
                  0.00000,    0.00000,    0.00000,    1.00000

vector = SharpDX.Vector3.TransformCoordinate(initial_orientation, rotation_matrix);

vector = 1.00000,    0.00000,    0.00000