The road channels are 160.455 (Buckingham Branch RR) and 160.95 (Norfolk Southern RR). These should go for Amtrak trains west and east of Charlottesville respectively. Most likely only your engineer and conductors are using radios, and this is where they would be tuned for all internal train comms.
Some of the sleeper trains may have radios for the onboard services people,(porters, food service, etc.) but I don't know if this is true of the Cardinal. If they have radios, they could be on RR freqs (not the road channels) or something else entirely. 160.92 might be worth a try. It's been some years, but if I remember right the EB and WB Cardinals meet in Charlottesville around 4p on Sundays.
73/Allen (N4JRI)