The only distinction between the Sonos connect, and the Sonos Connect: amp is that the connect: amp possesses an amplifier which powers to a limit of 55 watts per channel. The amplifier is an excellent add on to connect, and it enhances significant power to your speakers. Sonos has one of the most impressive reputations in the stereo game today.
The Sonos Connect: amp costs $50 extra than Sonos connect. There may also be a higher quality sound with the Sonos Connect: amp because of the additional amplifier.