Midi value 127 is 0 dB. What midi value is +12 dB?
This depends on instrument's volume range setting. You set this in Instrument Options->Controllers.
So in your case, you cannot reach +12dB with the volume range setting that you have set for the instrument you have loaded.
Thanks!
Well, I guess there's no use to change it, there are lots of instruments to change. Unless of course there's a script for changing this parameter on all instruments?
There isn't, this parameter is not accessible to KSP scripts.