"To begin with, get rid of Eurail - expunge it from your computer and don't use it again!!!"
Come on, Ken, you are a very prolific and respected member of this board, but that was not good advice. The Eurail (not RailEurope) website looks to me like it has very good schedule information, possibly as good as the Bahn's. They did show the connection you just cited from Lauterbrunnen to Monterosso. In fact, I think they might use the same database as the Bahn and several other websites use. No, they don't sell tickets for this route, but neither does the Bahn. But in this case, the OP already stated that they are using rail passes, so that doesn't matter. Eurail does show the trains on which additional "reservations" are required.
As for CaptainTrain, I pointed out to you in this forum (on my second post on 2/17), that CaptainTrain has serious flaws and should not be used for finding the lowest fares. I should also point out that CaptainTrain did not come up with that Lauterbrunnen-to-Monterosso connection, as did Eurail, the Bahn, and you. CaptainTrain suffers from the same terminal flaw as RailEuroe, in that they only show fares for tickets they sell, which is only a small subset of the tickets available, and the most expensive tickets at that. They don't include a lot of regional passes which could save a lot of money. However, CaptainTrain does not appear to tack on a commission like RailEurope does.