The PS-49 is a MIDI controller and thus does not inherently "sound" like anything.
You would need to configure a piano sound within Studio One.
For example, you could drop in one of the piano presets found in the Presence instrument.
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If you need help configuring your PS-49 to work within Studio One please see the link below:
http://support.presonus.com/entries/21728493-MIDI-External-Devices-Control-Surfaces-Setup
*NOTE: This guide is indicated for Studio One v2 but the process will be the same in v3.
