I can do no better than send you over to Iain Robinsons blogger where he has written about his visit to Sojiji, (where Rev. Master Jiyu-Kennett trained in the 1960's) to listen to some ancient music played, mostly, by monks.

Iain describes the music thus: "Gagaku is music to sit still with and experience, it is structurally so different that I can't describe it. But it's often a very meditative sound". Take a look, there are a couple of photos too.

Here is a link to a site talking about Gagaku music for those who want to read further on the subject.