If the ENT specialist tells you that the middle ear and the inner ear is not developed along with the microtia, then only you may need some assisted device, like BAHA. If the middle ear is well developed and there is only some conduction deafness, then a surgery on the canals can be contemplated. It needs a thorough evaluation like CT scan, MRI, BERA etc. All leading centres have this facility. Your local ENT specialist will be the best guide.