As a soloist he has performed twice with the wind orchestra of the Conservatory of Music in Ljubljana and twice with the Slovenian Philharmonics. He is very active as a chamber musician. As a member of different groups he has performed numerous concerts around Slovenia as well as across the Europe.
Apart from his busy concert schedule, Koren collaborates with young Slovenian and foreign composers and regularly substitutes in many professional orchestras, such as the Slovenian Philharmonic Orchestra, SNG Opera and Ballet Ljubljana, the RTV Symphonic orchestra, Slovenian Police Orchestra and Orchestra of Slovenian Army.
He also played in world renowned Youth orchestras – Gustav Mahler Jugendorchester (GMJO), European Union Youth Orchestra (EUYO) and three times as a member of Schleswig-Holstein Festival Orchestra (SHFO). His active cooperation with young generation of composers already resulted in premieres of several pieces dedicated to him.