Turn the plot cube around the X axis by 180°:
ilPanel1.Scene.Add(new ILPlotCube {
Children = {
new ILLinePlot(ILSpecialData.sincos1Df(200,1)[":;0"].T)
},
Rotation = Matrix4.Rotation(new Vector3(1,0,0), ILMath.pif)
});

You may want to further configure the plots axes.