Institute study material is more than enough for Auditing. Instead of spending time in reference books, u can study the material 3-4 times fully. try to answer the past 10 years questions from scanner. Try to remember some important section numbers.
There is no need to write sections in Auditing but to write the SA nos are important.If you cover the study module, it is more than sufficient.Just read the things conceptually rather than reading more and more.