Newbie: Kemper main out -12db button good enough? For FOH

I have an additional -12db on it (so -24db total) but my presets are a bit too loud.

-20db will pretty much always work in my experience.

I keep mine lower than that, as well. But don’t worry, if the engineer considers it to be too loud for his System, he’ll let you know

From the point of view of physics and electronics, it is always better to send the signal with a high output level and reduce the signal on the receiver side. The signal-to-noise ratio of the signal level is then better. So if the mixer has appropriate instrument inputs and / or attenuation switches, these should be used. Normal XLR inputs are often microphone inputs with pre-amplifiers. If you can bypass this signal path because you supply line level directly, it is always better. The fewer components there are in the signal path, the better and more unadulterated the sound. We have e.g. XLR combo sockets on the mixer board, these switch to instrument level when you plug in a jack plug.

So I always use a pair of Female XLR to 1/4 Inch TRS Adapter (Balanced) at the mixer input.,
or if the mixer has only XLR input some XLR line Attenuator https://www.audio-technica.com/en-us/at8202

Quote from Yoda Guitar

From the point of view of physics and electronics, it is always better to send the signal with a high output level and reduce the signal on the receiver side. The signal-to-noise ratio of the signal level is then better. So if the mixer has appropriate instrument inputs and / or attenuation switches, these should be used. Normal XLR inputs are often microphone inputs with pre-amplifiers. If you can bypass this signal path because you supply line level directly, it is always better. The fewer components there are in the signal path, the better and more unadulterated the sound. We have e.g. XLR combo sockets on the mixer board, these switch to instrument level when you plug in a jack plug.

So I always use a pair of Female XLR to 1/4 Inch TRS Adapter (Balanced) at the mixer input.,
or if the mixer has only XLR input some XLR line Attenuator https://www.audio-technica.com/en-us/at8202

This theoretically sound, but not practical for most live playing and also totally unproven how much of a noise difference there actually is. Have you heard this difference?

Most of the times these days I'm going through a relatively short cable into a digital stagebox anyway. The times when I'm not I'll be about as near to the mixer. The days of having to drive massive cable runs are really over (remember: your regular mics would need to do the same)

So no: don't interfere with what the engineer is plugging into his mixer, just give them a level that's decently workable and they'll figure it out.