Ok so to start off, here is my setup. I think that will help make things clear.
(Taylor 214ce)--(monster guitar cable)--(PreSonus audiobox 44vsl)--(2012 Mac Pro w/ retina display running garage band)
Now to my question. When i run my acoustic guitar to either one of the two instrument in's or either one of the two line in's i have been experiencing distortion with any sharp attack on the guitar's strings. I've checked and i am not clipping on the auidobox, master track, or the individual track that im recording to. Ive run my perception 120 mic through the same inputs and do not have a problem. Its not a major problem for me seeing as how i like the sound of a mic'd acoustic guitar over the piezo system any day, but i do sometimes like to mix a combination of the signals. Its just bugging me a little in other words. If anyone can help i'd appreciate it