PT92,
It's not necessarily complicated but rather frustrating and expensive. Butting heads with the Imperial Federal Bureaucracy is never easy.
I do think that taking the ATP check ride in an airplane with which you're already familiar is the best route under the circumstances. However, I'm not sure where one gets a stand-alone sim check ride in an ATR 72 or EMB 190. I get the impression the airlines operating those types don't sell type training to outsiders...and I don't know of any independent training organizations operating those sims. But I stand ready to be wrong.
Hang in there.