There may be no way to "say" the unsayable, and Huang Po's most celebrated student went on to not say it masterfully, beginning what became the Rinzai school. But if you want to experience perhaps the clearest, most accessible attempt at saying it, try John Blofield and Huang Po. The book is so disarmingly clear that one may believe one has "gotten it." Maybe it was just this (misleading) clarity that pushed Lin Chi into his famous antics.
This little book has a lot of wisdom. Sometimes it's a bit hard to grasp at first but it's nothing a little zazen wont fix. It's well worth the read if you're interested in Chan especially from the Rinzai sect as Huang Po was Lin-chi's (Rinzai)teacher.