We have been to a small town north of Turin in Italy twice - once via Eurostar, Paris, overnight in Basel (lovely place) and then to Milan and to Turin next day. We came back direct from Turin to Paris and the Eurostar. The next time we went Eurostar, Paris, and several trains (of decreasing gauge) to Chamonix, bus over/through Mont Blanc and then local Italian train to our destination. Back direct from Turin to Paris.
We went through the DB booking place in Surbiton, told them what we wanted, what free passes we would order and they did the rest in terms of reservations, Eurostar tickets and reduced fares for my OH for Switzerland - all done by email and a swift and very helpful and pleasant service. You send off the form with your requirements and they will come back with a quote (which you can then ask for a requote if your plans change before you book)
The only fly in the ointment is that now the service from Paris to Turin (and back) does not accept FIP coupons and you have to buy a discount fare. I'm not sure if this also applies to France-Spain journeys as well, but the DB people will advise.
If you need any more details on what we did, prices and links PM me
Enjoy your trip - it really is an underused facility