First number. Base layer speakers. Eg 2,3,5,7 are the common ones. Second number is subwoofers. 0,1,2 are common. Third is for Dolby atmos overhead/upfiring speakers, 2,4 are the most common.
Lastly soundbars are not suitable for any situation as they are incapable to match a traditional system with av receiver and speakers placed at specific angles for immersive surround sound.
Regards.