OK, well, a 500W amp is no joke. You won't be able to get a single-chip solution like you could for 80W or so and when a big amp goes wrong, it usually goes wrong more dramatically than a little one.
You posted a link earlier to Rod Elliott's site for the the PSU, if you look on his site you'll find this:- http://sound.westhost.com/project68.htm, which is a 500W subwoofer amp.
20-30 lines down the page it says explicitly in large red lettering:-
DO NOT ATTEMPT THIS AMPLIFIER AS YOUR FIRST PROJECT
You can get some help on diyaudio.com if you decide to push ahead.
I'd recommend that you buy the Dayton Plate amp though, and get your DIY fix by building a headphone amp or a gainclone. If you want something with a lot of parts, a discrete headphone amp.