Best amp for 4 Sonos ceiling speakers?

there are many solid state amps that have strong ratings into 4 or 2 ohms, which is what is needed, as the numerous pairs of speakers playing simultaneously will draw a good deal of current

i use a b&k av1260 amp that has 12 channels (stereo sets x 6)... built for the purpose such as yours, driving distributed speaker sets all over the house and outdoors - cost effective and well built

sound quality is ok, the speakers are not wonderful sounding to start with, just play background music, don’t stress over the ’audiophile quality’ of the amp, it just needs to be tough, deliver current, stay relatively cool

Whatever one works that you can afford.
I do not think that they will ever sound very good in series.