[PaulD]

stereos have an ingenious power regulation device, it's called a volume control. Remember, a 600 watt amp does NOT put out 600 watts all the time. The are also input sensitivity controls on an amp that help match the amp to the rest of the stereo.

Yes you can use a circular saw to build the box, but you better be REAL good at cutting straight lines (or like sanding a lot). A better choice is a table saw if you have access to one. You will also need a circular saw or router to cut the hole(s) in the top board for the sub(s) and any ports.

Always trust the manufacturers recomendations for box and port sizes, at least for a good starting point. They designed the sub and have a vested interest in making it sound the best. An experienced box maker may be able to tweak it a little to sound best in your application.