The ZP80 shows the same build quality and styling as the controller, though for a unit without its own amplification, it's perhaps a mite bulky. Still, Sonos has fitted it with a two-port Ethernet switch and a WLAN adaptor. The antenna's on the inside as is the AC adaptor, which is one of the reasons the ZP80 is as big as it is. I think Sonos has made the right decision - I'd rather have a ZonePlayer this size than a smaller device and a separate power block any day.
The ZP80 has digital optical and co-axial outputs for folk with up-to-date AV equipment, and it's installed analogue RCA jacks for those of us with older amplifiers. There's a pair of line-in RCA jacks too, handy for daisychaining other sound sources to a single-input amplifier, or to save you from having to switch the amp to a different input.
The line-in ports aren't simply for pass-through connections - each ZP80 can access another's input and play it back. Sonos bundles a RCA-to-3.5mm cable, and I used it to connect a Creative Vision:M to the ZP80 in the spare room and listen in downstairs in the living room. I switched the living room ZP80 over from my MP3 collection to the other box's line-in while I was walking down the stairs, such is the sheer freedom of using the wireless controller.
The ZP80 has its own volume control on the front, allowing you to leave your amp set high. You can adjust the volume from the controller too. You can also mute the ZP80 in situ or remotely.
The quality of the sound you get out of the system is largely dependent on the way your digital music collection is encoded - the ZP80 supports MP3, AAC, WMA, Ogg, FLAC, Apple Lossless, AIFF and WAV, so there's plenty of options, though as yet no DRM support - and on the amplifier you connect each ZonePlayer to.
Certainly, there's nothing inherent in the Sonos system to degrade the sound quality, at least not audibly. The tracks I played, covering a range of genres and codings, sound crisp and clear.