"I saw a link to subwoofer, thought, that sounds like a nice sub, dual 12's, 600 rms amp.. then saw MSRP of 2600$ and thought WTF?????"
i've always liked the way that sub looks. $2600 is a little rich, especially today, for that level of performance. that sub was sold at retail, which includes two levels of profit markup (one by the retailer, one by the manufacturer) the push-pull design is to help linearize non-linear drivers and isn't really needed if you are using good drivers. the epic 12 would be a nice driver to use for such a build.
the challenge with diy is that sealed subs rolloff and so typically need some eq on the bottom end in order to produce a flat response. that requires power and moves the drivers quite a bit, either of which could damage the driver. enter the frequency dependent limiter. this is a protection device that recognizes when the system is pushed too hard and simply "limits" the amount of power and the amount of excursion. most diy folks don't use limiters though and choose instead to use an amp that will run out of power before damaging the driver from over excursion and just keep an eye on the clip light on the amp to ensure that the driver isn't being fried with direct current that comes out of clipping amps.
so to beat the performance of the mk sub in the same form factor, two of the epic 12" drivers, a professional rack amp with about 1000 watts per channel, and an eq device will set you back about $800 + the price of the enclosure.
btw, there are other designs that will get you more bang for the buck, but the enclosures tend to be larger.