The heatube on the Giant Omnium has a different is larger at the bottom to accept a larger (1-1/4") integrated (I assume) headset. They make reducers that would allow you to use a standard untapered fork and special headsets that include tapered headset reducers that will reduce the lower headset size.

Edit: Here is an example http://www.bike.com/item/cane-creek-...et-cup/L10294/