If you are using the instrument input, try stereo recording (if it works, the instrument will probably come-out on the right).
And if stereo works you might have to dig through the Windows Control Panel to make sure the Windows mono/stereo settings for the AudioBox match the Audacity mono/stereo settings.
Or if stereo works, you can delete the silent channel after recording to make a true-mono file (which will play from both speakers).
Is there likely to be some ‘quality’ loss in the signal if just use the 'Speakers" option?
Technically it may not be as good but there may no audible degradation. You’ll be recording a “mix” with any other sounds your computer is making and also any optional sound “enhancement” adjustments that your computer might have (bass boost or other E, etc.).
The Audiobox interface is for recording from an analog source (a microphone or guitar/instrument). It’s essentially a high-quality “soundcard” with analog-to-digital (recording) and digital-to-analog (playback) converters. If you ever want to use a microphone, note that audio interfaces only work with stage/studio microphones. They don’t work with “computer mics”.