R1 powers a single electret mic from a filtered voltage. If you want more mics then two or three can be connected in parallel then the value of R1 should be reduced.
Also, because the Zen has NO amplifying at all, it requires quite a loud input to be just under clipping. If you'll excuse the non-precise comparison, it requires something similar to an MP3 player on 2/3 volume. So, because your circuit is a pre amp, it'll also need another amplifier afterwards, correct? Or will your circuit amplify the mic quite a bit more than I'm thinking?