Here is what I would recommend:
1) Read the Alpine owner's manual on all of the features of your unit. I have the CDA-7998 and, initially, I was overwhelmed with all of the features of the unit. After I understood the features better, I was able to get the system to sound MUCH better.
2) Turn ON your MEDIA EXPANDER (MX) feature. This is basically like a loudness button on most other decks...it will enhance bass, mids, and highs. There are three settings (1, 2, 3...at least on mine there is) and 3 gives you the highest OUTPUT change.
3) You have a 5-band parametric EQ. That means you have 5 EQ "slide-bars" that you can adjust the width (3 settings), the center frequency, and the volume of. I would recommend putting one slide bar at about 80 Hz, at the widest width, and about a 2 or 3 volume gain. Have another center frequency at about 120 with similar volume and width settings, and another at around 180 with similar valume and wide settings. You could also put another one around the 210 setting, if you would like. Then play around with the VOLUME, WIDTH, and center frequency until you are boosting the frequencies that sound best to your ear. NOTE: you can save these settings as presets #1-6 for future quick selection. ALSO NOTE: POP, ROCK, and DANCE songs typically will sound better with different settings, so play around a bit.
4) You have a Xover that you can set and I'm assuming you can set it for the SUB, FRONT, and REAR outputs separately. I would set the FRONT and REAR outputs at a crossover frequncy of about 60,70, or 80Hz with a -12db/octave slope.
what he said, i have the same unit as yours 9815 but no problem with it, sound quality is perfect
take it back to the people who installed have them check it out