"The Jane's Smart Art audio guide to San Marco is an adaptation of a now out-of-print book written by William Hood, the renowned Fra Angelico scholar. One in the series The Great Fresco Cycles of the Renaissance, Professor Hood's book treated the Fra Angelico frescoes of San Marco in the context of their religious, artistic, and historical significance."

This looks sounds interesting - and is available for $8.95 from the Jane Smart website. The audio contains a 45-minute background segment and 75-90 minutes on-site.