So for anyone flying into Rome that is not renting a car there are 2 train options. One is to take a train from Rome to Florence and then a train from Florence to Siena, then a short 10 min taxi ride from Siena to the Venue. If you want a faster but less known route you can take a train from Rome to Chiusi-Chianciano Terme then from Chiusi-Chianciano Terme to Siena. Both options are cheap but the latter saves about 30 mins of travel time and about 20 or so dollars per person. If you are flying into Florence then you have it easy and can take a train directly from Firenze Santa Maria Novella to Siena which takes about 1hr and 20 min and only 11 dollars. If you for some reason decided to fly into Venice you can take a train from Venezia San Lucia to Siena with 1 connection for around 49 dollars and 4 hours of your time. The train travel in Italy is absolutely amazing and extremely clean and efficient and surprisingly very roomy and comfortable despite the cheapness of the travel. We have spent more going a few blocks in New York on a lot less clean and comfy transport lol!
For anyone brave enough to drive you will take a coast road from Rome to the venue directly called the E80 which will take you approximately 2 hrs and 50 min.
Everyone will most likely have to take a car at one point to get from Siena to the venue and for that a taxi or shuttle is the best option. It is a short 12 min car ride from the Siena train station to the venue.