I usually play music between level 15 and 10 .
I assume you mean "between -15db and -10db". That's usually a decent level to get reasonable quality out of the system. The reason I ask is because I wanted to make sure the "noise" you described wasn't system noise from running the empeg too quiet with the amp gains set too high. Technically, you should be able to crank the empeg all the way up to 0db, and still be able to listen to the system. If not, your amp gains are set too high and should be decreased so you can get the maximum signal-to-noise ratio out of the empeg.
However, something you might want to try. If you like the way that the Alpine sounds through your amps, then you might want to re-route it so that the Empeg goes into the Alpine's aux-ins instead of the other way around. If you do, make sure to run the Empeg at 0db. You might prefer the way things sound that way. It's probably just a case of needing to EQ the empeg to sound more like the alpine did, but a quick work-around would be to plug them in the opposite order so that the Alpine is your tone controller.
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Tony Fabris