Won`t work I`m afraid. BS4500 can not distribute N.MUSIC, N.RADIO. If you press N.RADIO on your Beo4, it will activate the PHONO socket of your BM4500. You will need an audiomaster like BS4, BS3000, BS9000.
But if you just want to listen to your PC output, without any control, just connect it to a vacant BM4500 input and select this one in your link room.
Stefan