And a shotgun fired from sufficiently far away would have such a large spread that you'd only get some of the impact. If you shatter a comet fragment or asteroid sufficiently far from Earth, a lot of its mass will miss. Given that comets are not particularly dense, the gravitational binding energy of a comet of such sizes as the OP describes is not really that great, and a bunker-busting penetrator should be able to burrow many meters into the surface to maximize the explosive's effect.
The development of the spacecraft will take sufficiently long, I think, that not much can be done about the 1994 fragment, but in the aftermath of that impact, international outcry will demand that a constant anti-comet capability be maintained. That and a decade to rebuild Tsar Bomba and stick it in an armored shell should mean that the 2009 projectile is easily knocked out.
That said, the exact nature of the capability depends on where the 1994 impactor hits. If it strikes the North Atlantic, Kennedy Space Center is gone, so it's all up to Russia.
The 1.6 km impactor will be unpleasant, but not civilization-ending. Assuming it's mostly ice (comet fragment) and moving at 60 km/s and strikes the earth dead-on at 90 degrees, it'll kick up a tsunami many meters (or tens of meters) tall at a distance of 1000 km. The Pacific is the biggest ocean, so that's the most likely impact site--we can probably say goodbye to Japan, Hawaii, and most of the Pacific Coasts of the Americas, Australia, and China.