(The symbol of the Shin Oto Roku looks like this, but all white...trying to find a real pic of the symbol...)
The original Sound Five were the five most highly skilled ninja Orochimaru had found. They were completely loyal to his cause and to him...partially because of the Cursed Seals.
Some time after Otogakure was rebuilt, the diamyo of the Land of Rice Fields found out about this small group of highly skilled ninja and decided he would like to see what they would really be capable of. It was because of this that Shin oto Roku, the New Sound Five, was created.
Members of this organization are chosen because they are the best at what they do. This doesn't mean they are the strongest or fastest, or that they possess a strong bloodline limit, this simply means that they can more or less defeat any other shinobi in the village, no matter their rank, using whatever tactics they would use against their enemies.
As the name states there are only ever 5 members at a time, each, within the organization, known only by their position. Ichi, or One, refers to the leader, and should anything happen to him the next number takes over.
Ichi (One)- Leader
At any time a member can be challanged for their position by any other member, or any other Sound-nin. If a member is defeated, whoever beat them takes their place, and should the now ex-member wish to become a part of the group again he must earn it by doing the same thing.
The daimyo also has the right to change out members or rename positions as he likes.
Shin Oto Roku is the closest thing to ANBU Otogakure possess. This is because there is no official ANBU organization for the minor countries. This means that the members must do all that they can to ensure the safety of the daimyo as well as their village.
Within the village they are seen as a sort of guard against enemies, usually taking up positions at the four points of the compass to ensure no harm comes to the village or those within.
Unless on guard duty, or on an official mission handed down by the daimyo, they are free to live their life as a regular shinobi, taking missions and everything else, but, at any moment they might be summoned to preform a task.