Best step up device for low output Grados?

As I'm a fan of the Grado sound, I'd like to try their low output .5 mv options. However, I'll also either need to get a new phono stage or a step up device. I'd not rule out a new phono stage, but I'm not unhappy with the performance of the mm section of my Music Reference RM5III. Should I decide to continue using the Music Reference, what will work better for the low output Grados, a head amp or a step up transformer? The phono section of the RM5 has 36 db. of gain and the Aloia preamp I'm using has plenty of gain. I'm familiar with the counter arguments in regard to use of head amp/step up transformers with moving coils, but don't know if the moving iron designs present any new variables in this debate.