Both the AudioBox iOne and iTwo offer the features, high-end audio quality, and legendary PreSonus software integration that makes the i series special. Both are two-in, two-out audio interfaces with left and right balanced ¼” audio outputs and one headphone out.
Here are the differences:
The iOne has one instrument input and one microphone input. It’s perfect for a singer/songwriter who plays guitar or bass. The iTwo has two combo mic/instrument/line inputs, so it’s the way to go for recording in stereo with mics or a keyboard and for capturing duets, such as two guitars, two singers, or guitar and bass.
The iTwo has MIDI I/O; the iOne does not.
The iTwo also has a Mix knob that blends the live inputs with the return streams from the computer for zero-latency monitoring; the iOne has a fixed 50/50 low-latency monitoring blend using the Direct button.
Finally, the iTwo is compact and lightweight but the iOne is even smaller and lighter—a subcompact, if you will.
Otherwise, the features, capabilities, audio quality, construction quality, and included software of the two units are identical.