What I discovered is that there are a number of small "boutique" accounting/law firms in Italy run by American expats who are qualified to do IRS work and who serve other American expats. The big US/International accounting firms also often have a local operation in Italy that addresses expats.
The way it works for me is that I interact mainly with a 1 or 2 man/woman firm in Italy, give them all my info including all my bank and brokerage statements, W2 forms etc. They prepare my 1040 and submit it electronically, then they turn over my information (with all figures converted to Euros and after signing a confidentiality agreement of course) to an Italian commercialista they have a long-standing relationship with who prepares my "Modulo PF" tax form for the Italian tax authorities. They coordinate the 1040 and PF so that proper tax credits are taken under the US/Italy Tax Treaty.
The nice thing is that I don't have to do much, the bad is that it is a rather expensive arrangement, costing about 2000-4000 for the tax preparation alone. Also, Italy is, as my accountant stated with understatement in my first meeting with him, "not a particularly low-tax jurisdiction". A permanent resident is taxed on their "worldwide income" whether produced in Italy or abroad. A nonpermanent resident is taxed only on their Italian income.
I disagree that Milan is not a good location. My impression is that there are many American and British expats there. I happen to live in another big city, however. I don't have local knowledge.