New Sound System - Sound Issues

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Hi there. I recently replaced the factory speakers on my 07 (S) Sedan with atermarket and also added an amp to the circuit.

My main problem right now is the sound adjustment. So to be exact here's what I have in the car right now and what's not working right.
A. OEM head unit
B. Scosche SLC4 line out converter to amp
C. Infinity 475a 4channel full-range Amplifier (90 RMS)
D. Front Pair of speakers: Infinity Kappa 63.9i (3way-75rms)
E. Rear Pair of speakers: Infinity Kappa 693.9i (3way-110rms)

I've set the gain on the line out converter behind the stereo on half, also on the amp the gain in on 50%; so ~80% of the hissing sound is gone for now. But back to my problem which is the sound being to sharp (distorted like) which I think is caused by the frequency >>> For both pair of speakers I've set the FreQ to 80khz and yet when I listen to songs of all kind the sound quality is not crisp. It causes headache after listening to it for 10-15 minutes so I tuned the "teble" i think it was to -2 to make the sound a little bit softer and still it's not what it should be. Long story short is this problem caused because the frequency is wrong or is it becuase my speakers have different RMS rating than my amp.

Thanks in advance for taking the time to read this, even if you don't have the answer
Steve (San Diego, CA)