I got to say I have a nice boar bristle brush and fancy shave soap that I use along with my mach three seems to work well for me. My only complaint that by the time I shave down there and then my head I end up washing in cold water. And from personal experience I would suggest avoiding trying to use a straight razor down under. I don't know what made me think it might be a good Idea but it wasn't.
The boar bristle brush might not be "necessary" but hey, it has a tingle all it's own.