160.800 - AAR Channel 46 - is the CSX Main Line Dispatcher frequency. It is the fequency all trains - CSX, AMTRAK, etc. - use to communicate with the dispatcher while on CSX tracks. Here in Syracuse, AMTRAK trains always announce their arrival at and departure from the station on that frequency. They may talk with the dispatcher on that frequency at other times.160.070 is NOT an AAR channel. Inasmuch as it falls BETWEEN AAR channels 4 an 5, I doubt it is used by anyone.
161.070 is AAR Channel 64 and is used by CSX on some branches in the Buffalo area and on the three secondary tracks radiating north from Syracuse. It is also used by NS on some of it's ex-Conrail trackage, for example the Corning Secondary which runs from Lyons to Corning.
If there is a lot of traffic on the primary frequncy in an area, train crews talking to or amongst themselves may, by mutual agreement, switch to the alternate frequency provided they can still monitor the primary dispatcher frequency. The dispatcher never changes frequency: I doubt they even have the capability to do so.
I believe you will hear all you are going to hear from AMTRAK on 160.800. Remember in CTC territory, a train can make it's entire run without talking to the dispatcher on the radio!