When it comes to specs, the main difference is that the original DBD has an edge guard while the Infinity DBD has an edgeless design. Also, the DBD is available in 14 mm or 16 mm versions while the Infinity DBD is just 16 mm.
Besides that, they have basically the same build. This includes a hybrid shape, thermoformed construction, and Japanese Toray 700K Raw Carbon face.
In play, the Infinity is faster with a lower swing weight. It does have a smaller sweet spot than the DBD, though, so is a bit less forgiving.