The good news is that a BB386EVO crankset will mount to either of the bottom bracket types your CAAD8 might have -- English threaded or BB30. The 2014 Cannondale catalog shows the upper CAAD8 models with BB30 cranksets and the lower-end ones with square taper cranksets. If they're the same frame, then the square taper bottom brackets (like your Tange) are installed into a BB30 bottom bracket shell with an adapter.
The devil's in the details, though. If you've got a BB30 bottom bracket shell and an adapter for the Tange cartridge, you've got two options: (1) Remove the Tange cartridge and leave the BB30 adapter in place, installing BB386EVO bearings into the threaded adapter. (2) Remove the Tange cartridge, then remove the BB30/threaded adapter, and install a BB30/BB386EVO adapter directly into the shell. If you haven't had any problem with the existing bottom bracket, I'd be inclined to leave the existing adapter in place and install the BB386 crankset as if you were installing into a threaded bottom bracket shell. That way, you don't run the risk of damaging the press-fit bottom bracket shell surfaces while removing your original adapter.