We wouldn't be able to speak to sound quality, but it may be the case that a good external USB mixer might work very well with Studio One, depending on the model and the feature set. If you go that route be sure to do your homework to make sure...
1. The product works well with the latest version of Studio One.
2. It gives you the additional flexibility you require or expect above the AudioBox.
3. Last but not least, if it records more than two channels at a time, if you need that, if you plan to do that at some point.
Good luck in your search.