I agree with @dabbler. Speakers are normally driven by an amplifier, not a pre-amplifier.
Amplifiers output an electrical signal, at a low impedance to match the speakers, with enough voltage & current to generate sound waves from the speakers. The output of a preamp, by contrast, has a lower “line level” voltage & higher impedance—inadequate to drive all but the tiniest & tinniest speakers, but ideal for either recording or amplifier input.
Preamps condition or process the raw signal by various analog and digital means, including (in this case) digitally encoding a usb signal. No more analog,
@_Whitetigress, try to find usb-powered amplified speakers. You can squeeze a few watts from a usb port, while low-powered audio amps can be made small & cheap & you only need one cable. I see that your gadget has line-level audio outputs as well as usb, so you could go the conventional route of amp & big speakers. The “gain” knob should function as a master volume control in any case.