Since you have established that you had the ballancer replaced, did you personally inspect the old one for damage?

The tech says he hears a knock from within the engine. What do YOU hear?

A multitude of things could cause misfire. Fouled plug, Plug not tightened in head, Loose ignition wires, bad coil packs. Check the easy stuff first to elimate possibilities. Then move to the hard stuff like the crank angle sensor, cam sensor. At the same time you have the front apart you can check to ensure the belt was intalled properly and is not a tooth off of time.