Atma Sphere MP 3 pre-amp compared to

I have heard the MP-1. Suppose the MP-3 is at best as sensitive as the MP-1. The MP-1 is not a good option for low output cartridges unless a step up is used in front of the preamp. Otherwise, the sound will lack dynamics and nuance and have hiss. The hiss you might be able to ignore when music is playing, the dullness of the sound you will not ignore.

I have owned the MP3 with the phono for several years. It is a terrific preamp capable of outstanding sound. It is relativly quiet for a tube preamp but I doubt it will ever be as quiet as the solid-state, battery powered PHD. I certainly wouldn't call it a "step back". It has speed, transparency, air, bloom, and frequency extension in spades. Your going to have to decide if that's worth the potential of a little tube hiss.
FWIW. the preamp's stock chinese AT7's, in the phono section, are quieter than some highly selected NOS that I have tried and, IMHO, sound just as good.
Lastly, I agree with Tubes 108 that you should have the transformer option if you choose a cartridge with an output <0.5mv.

FWIW I use a ZYX Universe with the MP-3, which has a 0.24mV output. This is the setup we used at RMAF so plenty of people got to hear it. The preamp is equipped with the regulator option. There is no appreciable noise and no need for a step-up device.