There's really no difference between the two, besides the RMi series having a 3 more things included which doesn't even seem that helpful. The RMx is fully modular as well as the RMi. The RMi has Corsair Link which you can switch the rail you use from the default multi +12V rail to a single +12V rail (have not had any experience with it, first time hearing of it actually, so try looking for someone that has had experience with it or just call Corsair Customer Service), it also has a Fan test button, and for some reason a Mini-USB port... No clue as to why they put it there (Mini-USB to USB).