I use a Squeezebox at home, one feature you *may* find useful is that it can be used as a wireless bridge so I have mine connected to my XBox with a network cable and my XBox is online too.
You can use the Squeezebox to access internet radio (host PC or NAS doesn't have to be on for this to work).
You could get an additional Squeezebox Boom for the kitchen?
If you're after top sound quality, the Squeezebox uses Burr-Brown D2A converters (apparently that's a good thing) and it'll plug straight into a power amp yeah..
The SqueezeCenter software will send all of your iTunes playlists to the device but afaik it only supports one music source, so your lodger's music won't be available..
Hope this helps