Eurail Pass discount on overnight trains

I don't know if I would call it a discount, except that you don't have to pay the rail portion of the ticket (because it is already covered by the pass). The charge for the accommodations only is offered to Eurail and Interrail pass holders, Bahn Card holder, and holders of standard ticket for just the rail portion. To book just the accommodation portion, go to the Bahn website and find the train. Click purchase. You'll have to enter the ages and maybe click purchase again. That will take you to a list of the charges for various types of accommodations. At the bottom of the page will be a link to "book only extra charges". The next page will ask you for the type of rail coverage (pass, Bahn Card, or ticket), then you will see the charge for just the accommodations.

I tried again and could not find it still. It worked well on another booking i did last week, but it's not here this time...slightly different formatting, different options, etc. ...?

Sorry, I answered your question in general without seeing the specific train to which you referred. Did you even find an overnight train (ie, a night train) from Munich to Interlaken on the Bahn website? The only connection I find is from Munich to Salzburg (EN463/EN499) and then from Salzburg to Zürich (EN466), both night trains, then several day trains from Zürich to Interlaken. I don't think you would want to do that, even if you could, because you would have to pay for accommodations on both trains. However, because EN466 is apparently an Austrian run train, and doesn't stop anywhere in Germany, it is not bookable from the Bahn website. This is pretty far fetched, but if you put in Munich to Interlaken Ost with Saarbruecken as a stopover, it will show you a CNL night train from Munich (22:47) to Saarbrücken (4:56), then a series of day trains (EC/ICE/IC) to Interlaken. But I don't see that connection bookable for the rail pass "Aufpreis" only. Sorry Zach, I'm not having much luck finding a night train bookable on the Bahn site (and that Salzburg to Interlaken connection does not appear to be bookable on the Austrian site, either). You might have to call the Bahn.

www.rail.ch allows you to request reservations and price on the 23:40 to Salzburg, 01:40 departure on the Budapest - Zurich and connections forward from Zurich. You have to be specific about the type of sleeper, names, etc., and wait for a response. Spar fares available for a random date of 13 May.