Ive compared the Sonos to the Duet. They both have strengths and weaknesses. The Sonos is easier to setup and its mesh networking makes extending a Sonos system throughout a large home a breeze. If you need to extend the range of the system, you can place a bridge anywhere that you have an electrical outlet. The Duet also has the ability to be a wireless access point/bridge also. However, its harder to setup, and more expenses ($150 vs. $100) than the Sonos bridge.
When it comes to sound quality, the Duet has a slight edge. In addition, there are more options for modding the Duet, including adding upgraded power supplies. One advantage the Sonos ZP100 (ZP120) has is the built in amplifier; all you need to do is add a pair of speakers and youre done with a zone. In addition, the Sonos ZP120 has a subwoofer output. While its cheaper to pair a Duet with a Parasound Z-amp, which has better sound, it is not as neat or astatically pleasing. The Duet can easily be toggled off, the Sonos requires you to navigate through menus to put each zone in standby; I find it easier to just mute zones. Sonos units can be muted from the unit; the Duet cannot and requires the use of the remote.
When it comes to the remotes, its a matter of personal choice. I prefer the Duet remote because it is smaller and lighter and can be operated with one hand, and a thumb, just like an iPod. However, the screen is smaller. In addition, it slips easily into a pocket. The Sonos remote is larger and requires two hands to operate. In addition, its really too big and heavy to carry around in a pocket. The advantage of being bigger is the larger display screen. The Duet controller can be configured to become a digital clock when placed in its charging base. Finally, the Sonos has the ability to tie multiple zones together which is great for parties. Ive never tried this with the Duet, so I cannot comment on it.
Ive had no problems managing large libraries on either system. I have almost 2400 CDs and I can find any album in about 30 seconds on either unit. The Sonos software is easier to use and much more intuitive. In addition, Sonos technical support is quicker to pick up the phone. The Sonos supports Napster, Pandora, Rhapsody and Sirius services. The Duet supports Napster, Pandora and Rhapsody and Sirius support is in the works.
The one ability that the Sonos has over the Duet is the option to stream any analog source throughout the entire system. For example, you can plug an iPod docking base into the Sonos unit in the main system and listen to it in the bedroom.
So, it really comes down to personal preference when choosing a Duet or Sonos system. In my opinion, they are both winners.