Yes, I have two Squeezebox's V3, connected to my HTPC, Slimserver is installed. Music as OGG, MP3, MPC & FLAC.
The Squeezebox's are basically media streamers & VFD. You connect them into your LAN (or WLAN) They connect to your host with slimserver installed (PC, QNAP or Buffalo Linkstation Pro with Linux & Slimserver) and access music. Music can be on local computer, or on your LAN (ie on another PC or NAS)
They can play FLAC but not sure about apple. A CI was asking about Apple codec, I just recommended to ditch itunes/apple format for flac.
Can't answer itunes question, but it does have rescan/search for new music. You can add your own plugins, I'm using Custom Browser.
If you have more than one you can sync them to both play the same music, or different tracks. Audio is sent either analogue or digitally from your SB into stereo amp, DAC etc.
oh if your LAN is wired only, get the wired squeezebox. It's £40 cheaper. One of my SB is within 3M of switch, so bit silly using wireless.