I've shipped my bike via Amtrak Express once, and I'd do it again if I needed to, and everything lines up right.
I think that pretty much any Amtrak station that has baggage service can do Express. The big benefit to Express is that you get to use the ginormous Amtrak bike boxes to pack your bike. So all you have to do is remove pedals and turn handlebars, no need for the disassembly and reassembly you'd do using a standard bike shipping box via FedEx or UPS. You'll have to pay the standard box fee if you are using the Amtrak boxes, though, they are not included in the shipping price. I think I paid about $60 for shipping the last time I did it four years ago, you'll have to call Amtrak Express at 1-800-377-6914 (8 am - 8 pm ET, Monday through Friday) to get an accurate quote.
The big disadvantage to Amtrak Express is it's not a point to point service like UPS/Fedex. You have to go to the station to drop off the bike and then to the station to pick up. And you can only ship from/to stations with baggage service.