So...
Choral Casting (Sp): A choir of 2 to 6 zin gain a number of spell-like abilities, which they can cast at will. Each of the participating zin must be within 10 feet of another participating zin. The spell-like abilities depend on the number of zin, and the repertoire is cumulative (for example, a quartet can use the spell-like abilities of a duet and trio as well). The repertoires are as follows:
Duo: hold person, suggestion
Trio: charm monster, rage
Quartet: crushing despair, confusion
Quintet: mass suggestion, dominate person
Sextet: demand, irresistible dance
The save DCs are based on the highest individual Charisma modifier among the participating zin. In addition, one zin of the choir may make a Perform check to increase the DC (the other zin in the choir may use Aid Another actions to assist this check). If the Perform check exceeds DC 20, the save DC of the ability increases by +1. The save DC also increases by an additional +1 for each 10 that the Perform check exceeds DC 20 (a total of +2 at 30, +3 at 40, and so on). The caster level equals half the total HD of the zin choir.