[8] In 1992, he appeared at the Laxenburg Kultursommer, where he sang the "deftly smart" servant Peppo (in the original: Martino) in the Rossini opera L'occasione fa il ladro with "strikingly powerful bass-baritone excellence".
[9] In the 1992/93 season, he took on the role of Captain Sulpice in a new production of the Donizetti opera La fille du régiment at the Landestheater Innsbruck (director Kirsten Harms).
In the 1992/93 season, he also sang the bass-baritone part of Mustafa Bey in Rossini's L'italiana in Algeri at the Theater Orchester Biel Solothurn [de].
After his change of voice type, Sadnik initially sang in the role category of "lirico spinto", but finally expanded his repertoire to heldentenor.
In 2002, Sadnik performed the title role in Franco Alfano's Cyrano de Bergerac at the Opernhaus Kiel, where he appeared as Don Cesar in Reznicek's Donna Diana.
In the 2008/09 season Roman Sadnik made his debut at the Vienna Volksoper as Rittmeister Othmar Brandstetter in Ernst Krenek's Kehraus um St. Stephan [de], a co-production with the Bregenz Festival.
In the 2011/12 season, he appeared among others as Tannhäuser at Theater Bremen, as Der Bucklige in Die Frau ohne Schatten at la Scala (March 2012, conductor: Marc Albrecht) and in April/May 2012 as Laca in Jenůfa at the National Theatre Zagreb.
In January 2014 he made his debut at the Opéra Bastille as Nick in Puccini's La Fanciulla del West; his partner as Minnie was Nina Stemme.
In June 2014, he sang the role of Burgvogt Schweiker von Gundelfingen in two concert performances of Richard Strauss' one-act opera Feuersnot at the Vienna Volksoper.