The amplifier's datasheet uses an 0.47uF input capacitor, if this is already there you don't need the additional 100nF one in series. The trimmer is ok, you want it otherwise it will be to loud. If audio output is to noisy try adding a capacitor after the trimmer to GND to do a little low-pass filtering. I don't know a value but experiment in range of 100nF to several uF for best results.