Quoted from sparechange1974:
I can't speak to your exact concern on sound, however changing speakers makes a huge difference. Having done that, the game really came to life and sounds were clear and there sounds I had never heard before due to being drowned out. I don't think the stock speaks have tweeters. Here's a thread, $30 bucks gets you a nice set of kickers that bolt right in with wiring diagram as well. There is always the Pinball Pro or Flipper Fidelity route. The stocks ones definitely have to go.
With the new speakers, can you clearly hear the drawbridge lowering sound effect? All I can hear is the motor running while it lowers. Could you adjust your volume to about 4 and test it? Thanks for the advice. I will look in this thread for the speakers and wiring diagram.