The recording of the Main Mix to SD card on your StudioLive AR-series mixer is Post-Main-fader. This means that the level of the recording to the SD card is directly dictated by the output level of the mixer (as controlled by the Main mix fader and displayed on the Main Output meters). This is very important to keep in mind, because if your mixer is not properly gain-staged, the signal being recorded on the SD card will be too quiet, and not loud enough to achieve a proper signal-to-noise ratio and result in a good recording.
The first step of properly gain-staging your mixer, is to start with the input signal. While speaking into a microphone, or playing your instrument, at the same volume you expect during performance, turn the corresponding trim knob until the signal/clip indicator flashes red. Back down the trim control until you rarely see the red light flash.
Next, set your channel fader as close to unity as possible.
And finally, raise your Main fader while watching the output meters on your mixer. The output meters should fluctuate from "0" to "10" for best recording results.
Now that your mixer is properly gain-staged, adjust the level of your amplifier or powered speakers until you've achieved the desired listening volume. Never turn down your mixer, when you can turn down your speakers instead.
For illustrated instructions on gain-staging, as well as best practices recommendations, please consult Section 2 of your StudioLive AR-series Owner's Manual.