If i were to add a nother Ep-125 what would that do in terms of out put?

In terms of output it would increase the overall SPL of the room. You would have to adjust the LFE output of the amp to bring the levels back in line to the required level. The effect of adding the sub depending on your room size and configuration would be to balance out the overall sound stage and fill in any holes so to speak in the low frequency range.