I would go with a hifonics D class amp. Its 1600watts RMS x 1 at 1ohm. Oveously a 1ohm stable amp. Also the price just dropped to the same price as there 1200 watt amp. 199.99 which is only 50 dollars more than the MRP-M450 amp you were looking at plus gives you more RMS watts. The amp you are looking at is ok but it only has 220w RMS at 4OHMS and 400W RMS at 2 ohms. I think you could go with those if you bought two like you said but you would have to make sure you wired them down too 2Ohms to produce the 400w RMS a peace from each amp to power your 500w subs. Not to mention you would be buying two of them making the price $300.00. Its up too you but too me it makes more sense to get one amp for 100 bucks less that has more power.
http://sonicelectronix.com/item_6336_--+PRICE+DROP-+--+Hifonics+BXi+1606D.html
1-Channel Mono-Block Operation
1100 watts RMS x 1 chan. @ 2 Ohms / 1600 watts RMS x 1 chan. @ 1 Ohm
Super D-Class Topography
Ultra-Fi MOSFET Outputs
Illuminated Hifonics Logo
PMW MOSFET EXVP (Exponential Vari-Power Supply)
SPC Twin Turbo-Torroids with Simpatico Coil Design
Fully Adjustable Accu Cross
Crossover Includes:
24 dB Subsonic Filter (Adjusts 15 Hz - 50 Hz)
Bass Boost: Variable Bass Equalization (+18 dB @ 45 Hz)
Remote Bass Control Included
Balanced Line Inputs with Optional Hifonics MM-BLD-1
Gold RCA Line Outputs
Permits Amplifier Daisy-Chaining
4 Gauge Power Connectors
Dimensions: 13.77"L x 10.39"W x 2.63"H
1-year Sonic Electronix warranty