I just looked these up to find out more and figured I'd share the info and give you a bump:
MA-500
Amplifier Section
Continuous power output (RMS)
8ohm 20 Hz - 20 kHz <.05% THD 125 W
4ohm 20 Hz - 20 kHz <.09% THD 180 W
EIA Dynamic power
8ohm 170 W
4ohm 270 W
2ohm 320 W
Bridged mode (2 x MA-500)
Continuous power output (RMS)
8ohm 20 Hz - 20 kHz <.1% THD 360 W
EIA Dynamic power
8ohm 500 W
4ohm 600 W
Damping factor at 8ohm 200
Frequency response 1 W 10 Hz - 100 kHz ± 1 dB
S/N ratio 116 dB
Input sensitivity/impedance 1 V/30 k½
General
Power requirements 120 V, 60 Hz, 230 W
Dimensions W/H/D 35⁄16” x 51⁄2” x 173⁄4”
84mm x 140mm x 451mm
Weight 14 lbs. 6.4 kg.