A friend of mine went through this exercise a few years ago. From what I recall, the "i" changes included a new crossover set at 450Hz vs. 500 (you want the panel to go as low as possible), a new woofer, redesigned shape. I think the "i" is a bit tougher to drive, you need more current from the amplifier. He went back and forth and eventually chose the "i" model. He seems happy with them.
Good hunting.