The 1% distortion rating doesn't mean its producing 1% distortion at all times, it just means that's where they took the power reading. Its probably at less than 0.1% distortion at 95% of its peak power level. I have a XD600/6, with the gains set at about 25%, and Focal components/coaxials, and I find it plenty loud (and my car only operates at 12.8V).
Is there a specific problem you're chasing?
Is there a specific problem you're chasing?