my suggestion is to go through the articles and sub articles which are given in the tax portion of the syllabus by using the income tax ordinance and then solve the past papers, no need for a whole book, as you can see that there are very limited articles in the syllabus, and the calculation in the past papers is very very basic, i am an ACCA, what we used to solve for a part of 5 marks, is given to be solved for 20 solid marks
for audit you need to get a basic book of acca or ca and prepare only the relevant topics of css syllabus, ofcourse not the whole book