So you are recording a real acoustic guitar into an Audio track? If that's the case then the USB/MIDI connection will have absolutely nothing to do with that. Again, I really recommend checking out the GarageBand course video[s] on the difference between MIDI/Software Instrument tracks and Audio tracks..
As to why your acoustic guitar recordings may not sound good, well that depends on the specifics of the recording..
- Are you using a microphone or plugging a cable directly from the guitar into the interface? Recording acoustic guitar with a mic will always sound much better.
- If you're using a mic, what mic? How is the acoustic guitar miked up [position, distance, etc]? What are the settings on the interface mic preamp?
- If you're plugging the acoustic guitar directly into the interface, which 1/4" input on the interface are you using, Line or Instrument [should be Instrument] -- if it's the wrong one that can result in poor sound quality.
The presets you mention are only processing for the acoustic guitar signal -- they will not necessarily make the signal sound good if it's too poorly recorded to begin with..