With a globalpass it's included. Four types of train on this routes Railjet/Eurocity or Intercity/Westbahn and regional trains (RE5). Time difference between them is negligible. Seat reservations are optional on all of them, except the regional train. That is not possible to reserve. 

 No need to reserve a seat, just add "from Salzburg to München" in "My Trip" in the app. Tap the ledger just before you board the train, et voilà. Qr-code will generate. Ready to board and travel.

If this is your only trip by train, aEurail pass is a bad deal. You probably plan to take more trains? 

With a global Eurail pass you can travel as much as you like with the trains included in the Eurail offer in the 33 participating countries. 

Yep.  3 plus weeks.  Starting in Warsaw.  Prague/Krakow/Vienna/Budapest...plus small spots in between.  Octoberfest will be happening, so we’re debating if a “side” trip makes sense...

Then you're good as you are. Munich is at commuting distance from Salzburg, so you can just decide on the day itself if you wanna do it. Trains enough. :) 

Thank you.  As we move closer, perhaps I can indulge on things as they come up...