I thought I'd post a brief writeup of my recent purchase of the new Sonos Amp with the aim to help those on the fence make a call based on others' (admittedly subjective) experience.
The sound from the amp is fantastic. I have paired it with a pair of Bowers and Wilkins DM601 S3 speakers; previously paired to an NAD 3020 unit. The different is imperceptible to my ears. That is the highest of praise as the NAD is a fantastic amp too. There appears to be ample headroom with 125 watts per channel, though I haven't gone beyond 40% out of respect for my neighbors.
Good job Sonos.