It's too bad the PSR-S910's keyboard isn't satisfactory for you. I'm a big fan of the S910, and a chose it over the Tyros3 because I prefer a light and quick action on an arranger.

If you've been playing piano for 4-5 years, it's no wonder the keyboard feels strange to you.

You might have been better off with a CVP Clavinova, which has weighted piano keys, but it may be out of your price range.

Mid line arrangers, including Korg PA-500, Prelude and your S910 all have lightweight actions.

Ian