Differential Knock?

Just going though the pinout for the M150 and saw pins for Knock Differential positive/negative. Is this any different from just using a two wire knock sensor and pinning the signal to knock input 1 and the other wire to a 0V input?

Yes. You reduce the change of interference by using differential. Same sensor is used.

You can also wire it the "standard" way...and double the number of knock sensors, or use the inputs for something else if pushed on inputs.