The SM3 is a 3-way system (2 crossovers) and the EM3 Pro is a 2-way design. The drivers are of course also different, with the EM3 Pro drivers being much larger, and the one post I remember from someone that had their SM3 reshelled and had access to a SM3 reported minor differences between the two.
So no, they will sound different. The EM3 Pro is clearer, has more bass power with a little less warmth but better punch, the midrange is a little less thick and has less upper mid emphasis, and the treble is more prominent with better detail.
Ah. Thanks for that. Was trying to decide if I should get the SM3 or just skip it altogether and go for the EM3 Pro.