That looks like the two Mac Pros in the video are, respectively, an 8-core (2 x 4-core cpus) system and a 12-core (2 x 6-core cpus) system.
The answer is that building something like this (2x CPUs) is significantly more difficult than building a single-CPU system. For one, you have to use Xeon processors, which are much, much more expensive. You need a significantly more expensive motherboard. And since so many fewer people build dual-CPU hackintosh systems vs single-CPU... there's much, much less support.
That said, there are a handful of folks who have documented how to set up a dual-CPU hackintosh system, both here and at other forums. The cost advantage over a real Mac Pro gets slimmer with dual-CPU systems.
The more involved answer is that something like a 2600K (let alone the next-gen CPUs around the corner) will beat the 8-core system from the video you posted in all, or almost all, benchmarks and uses. Particularly if you overclock. Not only is the 2600K a newer generation, more efficient, chip, but it's 4 cores can act as if they are 8 cores... giving you an advantage in the small set of tasks that actually use this ability (like video/audio editing, VM, and benchmarks).
Even my i7-950 based system, overclocked to 4 Ghz, beats the 8-core Mac Pro from the video you posted. The 2600K SB systems are probably 20 to 30% faster than my system at identical clocks-- and can be overclocked 20 to 30% further than my system at moderate voltages/heats.
So if you need 8 threads, consider a current 2600K-based system for MUCH less than a Mac Pro or dual-CPU hackintosh. You'll save a ton of money and a ton of headache-- and there are tons of people using 2600K based systems, so you'll find a much more lively community. That, or wait for the 6-core 3xxx based systems coming around the corner.
Or if you're set on all those cores... go balls out, get two CPUs. But be prepared to have to really work to get and keep the system up to date and stable.
Good luck!
.., i'll keep looking around on th site & other sources.., maybe wait a bit for th release of th new E-systems.., im sure it wont be tht long b4 sum1 gets their hands on it..., also very curious as to how well it will perform compared to th 2600k...,