Studio One can open several other application project-file types. These include PreSonus CaptureTM Sessions (.capture), Steinberg Cubase Track Archives (.xml), Steinberg Sequel Projects (.steinberg-project), Kristal Audio Engine Projects (.kristal), and Open TL (.tl). To open any of these project-file types in Studio One, navigate to File/Open, and select the desired file.
I see that you have Studio One 2 Artist in your account. If you have any VST (effects or instruments) that your using in Nuendo, keep in mind that Studio One Artist does not support VST plugins. You'll need to upgrade to Studio One 3 Artist and purchase the VST Add-On or upgrade to Studio One Professional.
