going back for another two months ..what to see?

Find accommodations in another region you haven't visited yet since you've seen everything in Tuscany and Umbria and in general between Rome and Venice.
Puglia? Sicilia? Campania? Alto Adige? Piemonte? Plenty of more choices.
If Tuscan accommodations are firm and set in stone, see if you missed anything below:

http://www.borghiditoscana.net/#
http://borghipiubelliditalia.it

Have you been to Calcata? Lots of great small towns and Etruscan ruins in the area of Tuscia. My family is in Vasanello and we found at least a half dozen small towns and old caves and roads to explore. Friends have a fabulous tower that we usually stay in. I'd find a new apartment to explore other areas.

Just rub it in Jim...

I recommend, in particular, Camerino, Urbino and Macerata in the Marche region.

If you are venturing out of your base (which I highly recommend), consider a road trip that takes you through along the Apennines through L'Aquila, Sulmona, Benevento, Foggia, Matera and then end it with a stay in Lecce. The Adriatic side of the Apennines foothills is rather unexplored as well, with many interesting picturesque villages in Marche, Abruzzo and Molise.

The Mugello is not far: see (at least) Giotto's birth house and town and Scarparia. Follow the Via Santo Volto ( by car) from Lucca up the Garfagnana valley past Castelnuovo Garfagna into the Magra valley stopping at (at least) Filetto, Bagnone, and Pontremoli.

I recommend the trek to Civita di Bagnoregio if you've never had the pleasure. http://www.wantedinrome.com/news/civita-di-bagnoregio/ https://www.ricksteves.com/watch-read-listen/read/articles/italys-civita-di-bagnoregio-jewel-on-the-hill

I also really enjoyed Lucca near Florence - http://girlinflorence.com/2016/03/03/3-favorite-spring-destinations-outside-florence/

happy travels.

great suggestions folks .. thank you

I suggest getting totally out of your comfort zone for the first third to half of the trip. then back to a familiar place. check the discount airlines for one way nonstop connections and explore the world. no reason you can't spend 3 or 4 nights in Georgia on the way to Italy. expand your horizons.

back story here is that my wife is a professional artist. She has provided a package deal that includes cooking classes, personal painting instructions, group dinners, and winery tours. Five two-room apartments. They have all been filled. So this base ..Poggio Alla Croce is where I am. Train station is 15 minutes away in Figline. From there we can go anywhere. But, like having the car to tour around on my time schedule

Take a few days and go to Pulia.

See the sword in the stone at Tuscany's first Gothic church - St. Galgano http://www.athomeintuscany.org/2013/07/05/the-abbey-of-san-galgano-tuscany/

I have just the book for you. 'A Culinary Traveller in Tuscany' by Beth Elon. She is (was) a writer living in Tuscany for many years and her book is organized into ten itineraries by car based largely from Florence. She is decidedly not bucket-list oriented but rather sees and helps you discover the less famous sites and towns. She gives food and restaurant recommendations as well as recipes. She covers the Casentino, Lunigiana, the Mugello, the Svizzera Pesciatina, etc. We've done numerous of her routes and she's spot on. I suggest you supplement her research for a richer visit, and double check the recommendations as the book is almost 10 years old.

Mike .. great suggestion, I'll check that out ..and yes I visited that abbey

If you haven't, a few days and meals in Bologna. Some sights but many eats.