Can't comment on the Sky Box myself though my colleague at work says it sounds pretty good.
I have the Sonos Playbase, Sub and two Ones - I find the sound excellent and it's much more flexible than my previous 5.1 amp and speaker system especially with the night time and speech modes, no wires, no comlex setup, wife-friendly etc. Glad I changed to Sonos from my high end 5.1 system.
You should find the Playbar and 2x Ones ok - our TV room is about 220sqft - the main difference when the Sub was added is that is has more punch for movies and the Playbase seems clearer (possibly as it no longer has to supply bass frequencies)