[tptacek]

A combi oven does what you want: it creates a temperature-controlled humid environment, but uses steam instead of a circulating water bath. Unfortunately, they're extremely expensive.

You don't have to bag the food, for whatever it's worth. You don't even have to use water as your cooking medium; people have circulated butter for lobster. But the bag prevents the flavor from the product from leaching out into the cooking liquid and being diluted away.