You really shouldn't be looking at ATX power supplies for audio equipment. Nothing in this space can drive the 2KW max of that sub.
I have a silverstone 800w or 850w cant remember PSU driving a Focal solid 1 (1x500w RMS @ 2 Ohms) powering 2 JL Audio CP108LG-W3v3 soon to be 4, a Focal Solid 2 (100w RMS x 2 at 2 ohms) powering a set of Focal Access 165 A3 6.5-Inch 3-Way, and an Alpine headunit.
That setup runs for about 6 hours a day and has been running for just over 2 years on my toolbox at work. I try to keep the PSU's wattage above the total RMS of the amp/amps.