At the risk of beating a dead horse...
As our travel date gets closer we're trying to remove as much uncertainty as possible for getting from FCO to Siena. Our flight is scheduled to arrive in Rome at 9:15. We've been on the Baltour, FlixBus and Trenitalia sites. Baltour is a questionable option as it shows a 10:45 trip from FCO to Siena. This seems like a pretty tight schedule. FlixBus appears to be a non-starter as their offering is an 11:15 from Tiburtina to Siena.
Are we crazy to consider taking a Frecce train to Florence S.M.N. and then catching a bus to Siena Piazza Gramsci? It would seem that this would give us flexibility in case of flight delays, etc and should get us to Siena at a reasonable time. If this seems like a viable option we'd appreciate input on Frecciargento (FCO to Florence direct) versus the Leonardo Express to Termini and then on to Florence. The Frecciargento is appealing to us as we have never traveled by train before and will be jet lagged.
We'd appreciate any advice you can share to help make this a smooth move.