I went to Tempvs Fvgit yesterday. I've heard polyphonic sacred music before, but I've never seen it in a performance. What the group of six men did was to stand in a circle and sing. Which meant that each individual was singing in another person's face. It's sort of interactive, in the sense that you had to listen to your neighbour as well as yourself. And they had their arms draped over their neighbour's back or shoulders, so each person could literally feel the other breathing, and as they went on, you suddenly realised you weren't listening to six men singing but one organic entity with six voices. Lovely.
PS, this link might be better if you want a listen.