If you want to enjoy a folk show, Tunupa is an alternative, at the main square (Plaza de Armas). However the buffet is... just fine. I expected something better. If your main interest is the food itself, try the restaurants mentioned in the previous posts.

At Monasterio Hotel, Tupay restaurante offers opera performances with tenors and sopranos, on tuesday and thursday, but it's a very expensive restaurant compared with others in Cusco. I've never dined at Tupay but I share the info if somebody is interested.