The main difference is the height of the subwoofer. The RES 5 Flat has an installation height of 126 mm, whereas the RES 10A/P has an installation height of 150 mm. This makes the RES 5 Flat particularly suitable for shallow spare wheel wells. The RES 5 Flat is a bass-reflex construction with 2 x 130 mm (5") long excursion subwoofer chassis, the RES 10 A/P is a closed construction with the M10 Flat (10") subwoofer. The two amplifier modules are also different: the RES 10A has the AM300 (4 Ohm impedance) module, the RES 5 Flat, the AM300-2 (2 Ohm impedance) module.