IMHO.. sell one IDMAX. Put the other one into a ported box designed for your needs. Use the cash to buy a Soundstream TN1.200D amplifier (1050watts RMS at 2ohms, $200 new). This will give you similar SPL to 2 sealed, in fact with a better low end extension if tuned sufficiently low, and you will not need to wonder where to get a 1500watt amplifier on a budget.
My understanding running just 500watts to IDMAX may be a waste of an expensive subwoofer. Someone mentioned that according to ID people, IDMAX and IDQ sound the same up to 500watts of power. It's when you run significantly more than 500watts that IDMAX starts to shine (compared to cheaper IDQ).