There is nothing much more I can add to help you, you have been given the best information and help available. The Amtrak.com site has the same information as Amsnag, you won't get a lower price clicking through via Amsnag. The only suggestion I have is to check that on Amtrak, when you try to look at Roomette prices, make sure you don't hit the "change" button, as that will give prices instead for bedrooms!
I wish you all the best, just book on Amtrak. com.
I assume that you are in the UK, I have seen this :
www.
amtraktraintickets.co.
uk/
amtrak-
uk
Amtrak UK Amtrak - Now available by freephone in the
UK 0800 033 7810 begin_of_the_skype_highlighting 0800 033 7810 FREE end_of_the_skype_highlighting Whatever it is that you need to know about
Amtrak, we can help. Based in Norwich
...
I must state that I have NO KNOWLEDGE of this service, but you may care to try them. My own fear of "middle men" makes me deal direct with USA...
Let us know what you decide. You can even phone to america and speak to an agent and just ask the fares...
Ed