How do you buy the supplement for the night train? On-Line? We have rail passes.
That has been a challenge for me as well. I've searched all suggested sites and couldn't believe that the price I was being quoted on the Rail Europe site was correct (it is correct - about $110 USD per person for a double - with Eurail pass)! We decided to travel during the day instead as our budget is tight. But we still will need reservations to ensure a seat on this apparently popular route. I found BETS who will take care of the reservations/supplements, etc for a very small shipping/handling fee. Their number is 1-800-441-2387.