File format support is very, very good - you get MP3, WMA, AAC. Audible (Format 4) and impressively, Ogg Vorbis lossy standards. And if you’re serious about your audio quality, you’ll be glad to hear that there’s support for Apple Lossless and Flac, while uncompressed WAV and AIFF files will also play.
Pretty much everything Jon said about sound quality in his original review stands. How good a Sonos setup sounds will depend on a variety of factors. First and foremost, audio quality will depend on how your music is encoded - which codec you choose and the bit rate at which you encode. If you have enough disk space, using a lossless codec like Flac will take this step of the process out of the equation.
The second limiting factor will be the DACs inside the ZonePlayers, and although a serious audiophile like Jon will never be happy with the sound that the Sonos DACs produce, I honestly feel that the vast majority of consumers will be more than happy with the job done by the ZonePlayers in this department. Also, as with the ZP80, the ZP90 ZonePlayer features digital audio outputs in both optical and coaxial formats. This means that you can output the music as a digital bit stream, and use an external DAC - this way, an audiophile can stream losslessly encoded music around their house, while enjoying high quality playback through their own Hi-Fi equipment.
The ZP120 doesn’t have digital audio out, because it’s supposed to be used as a standalone Hi-Fi, a job which it does quite well. Again, true Hi-Fi buffs will probably be disappointed by the combination of Sonos’ DAC and amp, but the overall effect is far from offensive, and once more I doubt that most consumers would be disappointed in any way. Sonos sent me a pair of its own speakers to test with, which add an additional £130 to the price of the BU150 bundle, and although they produce reasonable sound, I’d suggest spending a little more on a better set, even if you’re connecting them to the ZP120. You can pickup some great bookshelf speakers from the likes of Kef for only a little extra.
The ZP120 is a far smaller device than the ZP100 that it replaces, despite packing the same 55 Watt output as its predecessor. The one compromise that has been made due to the reduced size, is the number of ports on the built-in Ethernet switch. Whereas the ZP100 sported a four-port switch, the ZP120 only has two ports, just like the ZP90 in fact. The Ethernet ports add to the flexibility of the system, allowing you to connect directly to your network if that’s convenient, while also allowing you to piggyback other devices on the Sonos wireless mesh. Let’s say for instance, your ZonePlayer 90 was sitting next to your Xbox 360 - you could get your Xbox online, by connecting it to the ZP90 via Ethernet, without having to buy a separate wireless module for it.