Not mentioned so far but when I've had students report this problem I give them two things to look for:
1) Balance in the mixer - everything set to 100 looks pretty but is seldom right! Some styles are just too darned loud, especially 3rd party ones, so maybe 85 for those.
2) Initial Touch Response - for most keyboard playing, Soft 2 is often the best choice. If you're playing a gentle sound like an Oboe, you're unlikely to hit the keys hard, but play more gently. This is a global 'set and forget' setting, so once done, it stays that way.
I'd look at these before diving into EQ settings. However, such diving may be needed if it's your hearing that's affecting things. As for tinnitus, I think a lot of musicians suffer - especially those pros who have been playing, and therefore listening, at high sound levels during their career.