the device address in Mervis is decimal (eg. "71" with all DIP switches on EMO set to "On"). The connection via I2C-Bus to UniPi is indicated by a LED below the address DIP switch. This is the hardware side. In Mervis you can check in debugging mode if your solution with EMO-AO5/12 works.
I cannot answer your question regarding HMI, because I only use the PWM channels 4-12 with PI/PID-controller.