I'm starting to have some doubts, as I haven’t used the Weekend ticket to travel to Salzburg in a while, so things might have changed.
As BR mentions, the Bayern-Ticket (
Laender-Tickets Info) will get you to Salzburg. It's cheaper too. You can buy a group ticket for up to 5 people, or a single ticket.
QUOTE
Bayern-Ticket (Bavaria-Ticket)Package price EUR 25 if you buy your ticket online or at the ticket machine. EUR 27 if you purchase your ticket at the ReiseZentrum.
This ticket is valid from Monday to Sunday for one day of your choice from 9 a.m. until 3 a.m. of the following day (on bank holidays for the whole day)on Saturday and Sunday and bank holidays from from 0 a.m. until 3 a.m. of the following day. It can be used on all local trains (Interregio-Express, Regional-Express, Regionalbahn,
S-Bahn) and the entire transport system in Bavaria as well as the Münchner Verkehrsbund (MVV) and Verkehrsverbund Nürnberg (VGN), Augsburger Verkehrs- und Tarifverbundes (AVV) and many more.
Bayern-Ticket Single (Bavaria-Ticket Single)EUR 18 if you buy your ticket online or at the ticket machine. EUR 20 if you purchase your ticket at the Reisezentrum. This offer is only for one persons, same conditions as Bavaria-Ticket.