Drive from Amboise to San Sebastian

You are referring to San Sebastian in the Basque region, just over the border from Bayonne, FR, is that right?

The drive would take pretty much a full day. If you want to visit Angouleme, which many tourists enjoy, you can take the secondary route from Poitiers to Bordeaux instead of staying on the A10, but it will be slower. After you leave Bordeaux, you go through the Parc Natural Gascogne.

Here are routes and a map from Via Michelin. You'd really have to devote a full day to the drive. Roads in France are great but beware of the speed cameras.