PreSonus did not make the Huxley M-49, however we understand it is similar or the same keyboard as the PreSonus PS-49 which is in the list of device in External Device Setup.
Follow this tutorial on how to setup external MIDI Controllers in Studio One, the method has not changed for basic controller setup since the very early days of Studio One, so don't be put off by the v1.6.5 shown in this video, the setup is the same.
http://support.presonus.com/entries/21004253-Obedia-Studio-One-Setting-Up-External-Devices
When it comes time to select your device, open the PreSonus folder in Studio One 3 OEM Artist and select the PS-49.
