I'm finding Venice-Munich advance tickets for as little as 48 euro on the OBB website, 50 euro on bahn.de.
It might be worth just booking the darn thing instead of paying for supplements in Italy and Germany, and a ticket from Brenner to Mittenwald (assuming you want to take the fast train).
Also, there's one train that's direct from Venice, without having to change at Verona. The prices I quoted are for this train. 1:50 pm on a random date in late August (Oct-Nov won't be on sale yet). Comparable pricing for the Verona-Munich leg on most other trains--you'd have to get to Verona on your own dime/pass.
One other potential upside of the ticket from Venice is that trip wouldn't count as one of your travel days on your pass, if that's a consideration. Fastest too at just over 6:30 travel time. Time for a final lunch in Venice?
just tossing out ideas...
