PreSonus offers no "personal mixers/mixing systems", but for a basic set-up you need nothing more than a headphone amplifier like the HP60 (6 stereo channels) or the HP2 (1 stereo channel). The HP2 allows a direct connection via the included XLR-adapter, but needs 9V (battery or power supply). Musicians can also use a small mixer like the StudioLive AR8 (or even smaller!). This is a perfect solution for drummers and keyboarders, as they can feed additional signals like click into their in-ear mix. For singers a wireless solution probably makes more sense. By adding a RM32AI and AVB or Dante network some day, a CAT5 cable would replace the multicore (stage snake) and you could use 16 auxes (instead of 14, which then are additionally available at FOH). Mixing is done by "QMix-AI" on iPhone or iPod touch or "UC Surface" on iPad. You can start with one iPad on stage and one of the musicians taking care of the monitor mixes.
SL 3242AI -> multicore or network -> headphone amp or mixer -> musician
SL 3242AI -> multicore or network -> headphone amp or wireless device -> singers