Depends your scenario. For straight up, affordable amplification, it's the XLS Drive Core. For affordable, DSP controlled, higher wattage it would be the XTi2.
For no holds barred Class A type, but more efficient, higher than Class A wattage it would be their I-Tech HD.
The I-Tech will need to be housed outside the listening area since they have loud fans.
For distributed audio it would be the CE series (70 volt).
What problem are you looking to solve?