You can route all your drum mics to Groups 1 and 2, then use just two faders to control the entire drum kit volume.
Aux 1 and 2 are typically pre-fader (for monitors), while Aux 3 and 4 are post-fader (for Reverb/Delay). Soundtracs Topaz 12 4 Manual
The Topaz uses an external PSU. Ensure it has plenty of ventilation, as these can get warm during long sessions. You can route all your drum mics to