The Innenraum day ticket costs €6,70, and the 3-Zone ticket you would need to get from MUC to the Innenraum costs €8,70. That is already €2.40 more than the Airport day ticket. The other option, if you need to travel at all on Day 2, is a 3-day Innenraum ticket, which costs €16,80, plus two single 3-zone tickets (total €17.40), which brings your total to €34,20. . Even two Airport day tickets plus a single Innenraum day ticket for day 2 works out to a total of €32.70, So you are better off with two Airport day tickets and single tickets or an Innenraum day ticket for day 2.