Thanks for your reply. We are planning a few days in Munich and Budapest before/after (or vice versa), so thankfully we won't have to worry about getting a very early start to/from the airport.
Unfortunately, I'm unable to access the link to the thread you posted because it says I do not have permission to read it. I'm new here, so I'm unsure as to why that would be. Perhaps you could post the title and I could search for it?
I'm still having a hard time determining if the Budapest to Passau sailing goes through the Danube Bend during the day. Even the Viking travel consultants I spoke to could not give me a definitive answer. It is not specifically called out in the itinerary, like it is on the Passau to Budapest itinerary.