Simple "rule of thumb" explanation:
When working with power (measured in watts): +3 dB is double the power, +10 dB is 10 times the power.
Power amplifiers actually amplify voltage, voltage x voltage/impedance =power in watts.
When working with voltage or current: 6 dB is double the voltage, 20 dB is 10 times the voltage.
The chart indicates the input voltage required for the amp to reach it's rated power at 1kHz with various voltage gain settings with the front panel gain set to "0dB" (fully clockwise).
The amp does not limit voltage or current in the 8 ohm 2 channel mode, but does limit into lower impedances or when all channels are used.
Wizardry aside, 41dB of gain is the amplifier's most sensitive setting, requiring the least input voltage for full power.
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If you want the amplifier to be driven to full output with only 1.41vrms, (+3dBv, or +5.2dBu) then you would use the 41dB gain setting.
All that said, how you want to set your DSP gain structure and limiting for a DJ system depends on the mixer's output and your preferences.
[URL unfurl="true"]https://sengpielaudio.com/calculator-db-volt.htm[/URL]
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