Where are your speakers connected?
If they are connected to the computers outputs (e.g.the kind of computer speakers most people may have at home and workplaces), Studio One will not recognize them through the interface.
You select speaker (and/or headphone) outputs through the interface - so if you want to use the computer speakers, they must be connected to your interface (although I doubt that's possible, as interface would take a 1/4" plug and computer type speakers are usually 1/8" plugs).
You will then also need to configure your interface 'song setup' so that you are able to select the outputs you want.
Another possible option may be to select the computer's sound card itself as the 'interface', but if that's even possible, you'd be required to run your recording inputs to the computers mic input.