The Amira is meant as an aggressive race-oriented bike. The Synapse is a more upright, "endurance" (read "relaxed") road geometry. A "plush" bike, if you will. What do you want to do? The carbon layup may be a little different, and the Amira is probably going to feel more stiff. Helps on climbs and in going fast, but may not be as comfortable over long rides.

The components are about the same. I don't know about wheels.