Where did you get those sizes? On empeg's site on the "tech" link it says:

Physical (maximum)

Docking unit 2 inches (50mm) high
7.2 inches (183mm) wide
6.8 inches (173mm) deep

Head unit 2.2 inches (55mm) high
7.3 inches (186mm) wide
6.0 inches (152mm) deep

I'd assume the head unit, the bigger one, is what you should quote as the size. The docking unit goes into the head unit, no?