Power Core RP v2 provides mic preamp control from a dedicated page in VisTool RP. 

Mic/Line Card Control

If a Mic/Line or Studio IO card is installed in the Power CoreRP, the slot containing the card will be activated and the channel preamps can be controlled.

Touch on a slot to select that IO card. Selecting a slot will allow you to adjust the Mic Gain, Pad, Phantom Power, and High Pass Filter. 

The PPM meter to the right of each channel can be used to monitor the input signal level.

To preview the audio signal, press the PFL button to the right of the meter.

The Mic Pre page PFL bus uses the Matrix PFL output.

A__Mic8 Preamp Control

If an A__Mic8 connection has been enabled (using the Emberhosts.ini file), and the A__Mic8 is online, the slots will be enabled and the mic preamp channels can be controlled.

A__Mic8 units do not have PPM meters or PFL capabilities.