My wife & I have Eurail Global passes. There is an overnight train that leaves from Berlin at 19:25(we would be boarding in Dresden at 22:10) that arrives in Vienna WestBahnhof at 6:22 a.m. I'd like to reserve either a couchette for myself and wife or a sleeping compartment for two. I would like to find out what the cost differences are and make the reservation here, rather than wait until we get to Europe. For the life of me I can't figure out how to do that. I look on RailEurope Website, but searches cannot locate this particular train. The http://reiseauskunft.bahn.de/ Website finds this particular train and offers options for couchettes and sleeapers, but looks like I can only buy full-fare tickets. Since we have Eurailpasses, we just need reservations for the trip plus the extra cost of the couchette/sleeper compartments. And I can't figure what that extra tariff would be or how to purchase just that component.
Can anybody help?