S2 is the software powering a range of Sonos speakers. You’ll need to be more specific.

Sorry, I have the sonos amp, arc, sub and 2 s1s I want to add 2 speakers for music through the amp, I was wondering g if it would sound better with 2 s1s or the kef q150s?

There isn’t an S1 speaker. Do you mean PLAY:1s, or Sonos Ones? S1 is an operating system. 

Speaker sound signature preferences are very subjective and for speakers in the same class by price points if no other way to decide the class is possible, only by listening to both yourself will you get a reliable answer to this question.