I remember talking to Jim McQuiston of CBS Facilities Engineering several years ago about the tracks below Broadcast Center. He told me those were old unused railroad tracks that connected to the West Side Freight Yards. Perhaps the old station referred to was an old underground freight station for the building's former tenants. I don't think the NYC Subway tracks ever went that far west in Manhattan but I could be wrong.
I also recall that CBS had a storage facility across the river in New Jersey where various program media were stored. What happened to this facility I do not know? Maybe this tidbit will jar someone's memory.