英文长难句的分析.if it is essential for the listeners to understand

{If it is essential for the listeners to understand the musical style [as applied to a composer's work],it is even more so for the interpreter.
it is essential for sb.to do sth.
as applied to修饰前面的musical style
so 指代的是前面的essential.
it is essential for the listeners to..与 it is even more so for the interpreter这两句的结构并列.
再问： 这里的as词性是什么呢