The Connect (aka ZP90) is a digital wireless transceiver that is capable of bringing all your music sources into any existing music system with an auxiliary input. These sources will usually be your hard drive music library such as iTunes, but can also be (i) Internet Radio, (ii) online libraries such as Spotify & MOG, and (iii) a source directly attached to any other zone, which might be a CD player, for example. You could say that the Connect turns any existing system into an independant Zone controllable by the Sonos controller. Note: You'll probably also need a Zonebridge to connect to your router.
The ultimate quality is then only limited to the system you play through, and the source files. For those seeking a higher level of performance again, the Cullen Mod version of the Connect has enhanced digital processing onboard. If you have a high quality system you may elect to go the higher level Connect as well.
Another enhancement to the Connect comes in the shape of the Arcam Sonlink, which sits neatly under it and gives a DAC upgrade to the outgoing signal.