You might want to check your manual for what is the “unity gain“ setting of the PA inputs. Basically, what this does is set your PA up so that it isn’t attenuating your input signal, nor is it boosting it which may introduce some additional noise.

Now try adjusting the volume with the keyboard’s outputs and see if that gives you sufficient volume for the venue. This should, in theory, give you the best signal to noise ratio for your system overall. There is nothing to gain by putting a super hot signal in and turning it down, but there is plenty to lose by putting a too quiet signal in, and then boosting it with additional amplification. Essentially, you are shooting for the PA to work at its optimal level, which is usually the unity gain point.

Generally, most arrangers do not introduce additional noise unless it is in the last 10% of the volume knobs travel. I’d generally tend to not try to push the keyboard past the 75% to 80% volume points. But at unity gain in most PAs other than really, really small ones, this is MORE than sufficient for most gigs.