I know you say the amp is not clipping, but was the output checked with an oscilloscope or DMM? Also, the only accurate way to check for clipping is with the system loaded from my understanding...in other words with the speakers hooked up. Not calling into question your audio abilities, just wanted to make sure everything was out in the open for diagnosis.

Also, not sure if Alpine sends a "birth certificate" of real world tested output or not, but maybe you have a freak amp putting out way more than spec'ed.