Usually you do not want "everything from a book (meaning photographic recall - that is usually not all that worthwhile). You say that you initially buy a book because the cover appeals to you. Fine. Ask yourself "why?", "what about the cover interests me?", "what might this book contain that I am interested in?". You now have an initial goal that is not super specific, but has a certain level of specificity that can start to help directing your mind towards your goal of understanding the book. As you prepare you learn more about the book - it's structure, some more details about what it is about, and things might start to jump out at you that you would like to know more about. This is great - you can now redefine your goals in reading the book with a greater level of detail. After you PhotoRead the book and allowed it to incubate, you start super-reading and dipping, perhaps based on some initial questions that you have formulated from your previewing. As you learn more from super-reading and data-dipping, you narrow in more closely on the things that really interest you in the book. Finally, when you mindmap and (maybe) super read, you really zoom in on the specific areas that you want the finer detail of.
The process, as far as I understand and apply it, is one of continually refining/redefining your goals as you go from ignorance of the text to mastery. Since you are making a number of passes through the material, fine tuning your goals for that text should become easier and easier.
PhotoReading is a purpose-driven activity, and is not (I believe) designed to be completely passive. The actual PhotoReading step might be passive as you absorb the text, but both prior to and after that stage, the PhotoReader is a very active and demanding reader who is constantly shifting mental gears and readjusting to their greater knowledge of the text.
