If you are on a Windows machine, please install a free program called ASIO4all on your system to use as the audio driver for your Blackstar amp. You can download ASIO4all from the following link:
During the install of ASIO4all, make sure to place a checkmark to install the Offline Settings. Once installed, you can open Studio One and go to Studio One>Options>Audio Setup and set ASIO4all as your audio device. Once you have set ASIO4all as your audio device in Studio One, you will see a small icon of a play button in your startup tray (next to the clock in the Windows status bar). If you double-click this icon, you can choose the devices on your system that you would like to be communicating with Studio One via ASIO4all. Here is a screenshot: