John. The airflex does have a single port on the back for a booster so it would be behind your main machine or it could be inline as the norm. The one in the vid is interesting but I see it uses two ports. What happens if they are linked into a single port? I did toy with hooking an alltec pro plus into the airflex port just to see what happens Though it's hardly practical as a usable solution. Perfectly happy as I am but if you have kit lying around and like a tinker it can be fun.
I'd say the back port on the airflex is more for easy connection to they're external exhaust more than for a booster ... if u connect your twin vac to that port u will get some lift increase but as both machines are parallel u will not get benefit of two motors as shown in the vid ... you will if you just put a Y splitter between the two machines and just run them side by side .
In the mytee vid each motor in the main machine has a port from its exhaust , they are then connected to two more motors , so you have two in parallel in front connected to two in series behind ...
also the motors in the above are electro 5.7s hence the 300cfm ... if u did that with two regular 5.7s u would get about 220 " lift and 230 cfm or there about .
shows drop after long hose run , but still useable
http://www.youtube.com/watch?v=iXeEa6MKLwA