I have played around with an S70 controlling a squeezebox, but it was done through the web browser interface, not adding it as an IP device.

If you go to the downloads section of the dealer site, there is a document that shows you how to set this up; it's pretty easy.

Since the squeezebox is open source, I'm sure there is a way to add it as an IP device and do some cool stuff there (like maybe with Nevo Widgets), but since I don't use squeezeboxes that much, I haven't looked into it.