05 Mitsubishi Lancer, Alpine cda-9830

I just traded my 05 Mitsubishi Lancer in for a better model 05 Lancer. This one has the sun and sound packace, which includes a 315watt infinity 7 speaker sound system. I want to install my Alpine cda-9830 hu in this car, but there is no hook up for the factory amp and sub. I tried an aftermarket adapter, and the system sounds like garbage compaired to what it sounded like in my other car with only 4 speakers. I was told because when using the rca connections the Alpine hu amp is disabled using only the factory amp which is designed to only power the sub in the trunk.
I was also told the only other way to use my Alpine is to by-pass the factory amp and sub and not use them at all, using only the remaining 6 speakers. Is this true or am I not understanding something here? If it is true, how do I rewire to by-pass the factory amp and sub?

Bump!