Squeezebox Internet radio 'sputtering?

Your speed is more than adequate, but your connection is obviously breaking up somewhere in the chain. My first thought is that your router is the culprit, or possibly your ethernet cable. When you say you're using a Squeezebox/Duet combo, do you mean just the Duet, i.e. controller and receiver? Also, are you accessing the streams through Squeeznetwork or Squeezecenter?

I would suggest going over the Squeezbox forums and ask for help.

http://forums.slimdevices.com/

Thanks for helping out here.
I can exclude the Ethernet connection from the router as the 'trouble maker', because the sputtering also happens with the wireless connection. I am using a Duet with receiver. I have Squeezecenter open on my PC when I listen to Internet radio, but I frankly don't understand the function of Squeezecenter or Squeezenetwork in this ordeal. The forums you have pointed me to mention similar 'sputtering' problems but I cannot see a clear reason or remedy for my system yet. Why does 'speech' such as announcements ALWAYS break up/are scrambled?

Have you disabled the firewall?