Originally Posted by gemac

What I couldn't tell from your original post was if the flight you missed (on "a non-AA carrier" was part of your original ticket, sold to you by AA, or was it a separate ticket?

If it was a separate ticket, then AA got you to your destination (MXP, as far as they were concerned) 6-7 hours late. Standard compensation for such a delay, if caused by mechanical, would be 5,000-8,000 miles, so you are in the range already. By continuing to protest, you might get AA to declare it mechanical and cough up an added 2,000-3,000 miles, or maybe not. Whether it is worth it to try is one of those YMMV things.

Continuing with that assumption, your subsequent difficulties (the missed flight on the second ticket, the fact that the carrier had no more flights for two days, the fact that you had to take the train, and the fact that you arrived at your ultimate destination 27 hours late would fall into the realm or your problem, not AA's.

On the other hand, if you bought one ticket from AA connecting in MXP to your ultimate destination, then AA delivered you to your destination 27 hours late. That is a whole different thing, and AA would owe you substantially more compensation, IMO.