"Stop" the SB (or turn it "off") before you stop SS.
If you forget to stop the stream first, you can reboot the SB (hold the
Power button on the remote) to stop the stream.
If you want more independence from SlimServer, you might look into
tuning the Internet Radio station through SqueezeNetwork
I'm connected to my SB via a linksys wireless router which has been
working great. One thing I love, by my wife hates, is that after
powering down the box the SS is running on, the SB continues to play.
I think this is a nice feature in that in the morning, I'm still
connected the Internet Radio