The simple answer is that a relatively inexpensive electric piano cannot (and isn't meant to) compete with the kind of sound quality you're going to find on a grand piano.I started on an electric piano that was pressure sensitive, but nowhere near as sensitive as any acoustic piano would be, grand or otherwise. From your description it seems like your piano is not pressure sensitive at all, it will make the same volume whether you press lightly or slam down. There's nothing to be done, short of making the investment in a pressure sensitive keyboard. These typically start at around 900 dollars on the low end from my experience but you can probably get one cheaper used. Depending on your goals, it may be in your best interest to make this investment. If you want to play with more emotion and feeling, you'll need a piano that can respond to variances in touch. If you begin to learn more advanced pieces with quick, difficult sections this will become more of a problem. Since little pressure is required to get that sound, you never develop the necessary strength to play loudly on an acoustic piano. I had this problem when I was adjusting to playing the Steinways in the practice rooms at my school and it was a struggle!
I recently upgraded to a very good digital piano, since I'm advancing, the Kawai CA97. You probably don't want to go that fancy. I had a Yamaha CLP 320. It is touch sensitive, but I had to push the keys almost to the bottom before they emitted a sound. When you have to push that far down you get into the habit of keybedding, and that in itself will create a clacking sound.