It has to do with the voltage difference between the panels. The more cells in one panel, the higher some voltages (like Voc and Vmp) are and the current micro inverters don't really like that. Enphase has a calculator available so you can check if the panels you like are compatible with their micro-inverters. I've also noticed they started supporting *some* 72 cell panels. 96 cell panels are still a no go though. (effectively meaning you still cannot use SunPower panels with Enphase)