you cannot use two amps in his application, three subs makes the full 4 ohm load correctly.

HONESTLY I would have looked for something like an MTX2300x
that is rated @ like 600x1@4 but will do ~900-1000w @ 4 ohms given 14'ish volts. I had one on a pair of old JL 12W4-d4's and it was honestly my absolute favorite set up of all time...