| I have the TC flavor of this box. It works with a bass about as well as with a guitar. Fingerpicked guitars, for example, don't work so well. It needs to be able to figure out what the chord is. So if you stick to the root with bass, you're fine. Strummed chords are really what it's meant for, and it can figure out not just the root, but whether it's major or minor. Very cool, actually.
The problem with plugging in a bass is that is if you were playing, say, the notes of a major chord as a simple bass line, it would interpret each single note as a new root and change the harmonies accordingly. So if you were triggering it playing bass, in the harmony vocal parts of songs, you would need to keep the bass very simple.
Best bet would be to get a rhythm guitar player who sticks to the actual chords to plug into the box! | 
