In my opinion, there are better alternatives such as the much smaller, lighter and just as powerful amps.
Example:
The little one replaced my big and heavy one. Have no regret, and happily handed the 60 lbs amp to someone younger and stronger.
Aside from that, I know you didn't ask, but I am curious to ask, what are you trying to gain? If the AVC-X8500HA has more than the voltage and current you need, it doesn't matter if you replace it with two 2,000 W monoblock amps, they will just be extra dead weights.
If it is about "sound quality", it would be a hot topic that has been debated for years. Just keep in mind amplifiers are designed to amplifier the input signals without introduction any form of distortions, only believe the "better sound quality" claims if you can find scientific provable reasons.