I don't know if I've heard the specific QSC Model that your asking about, but the ones I have heard are the 3way powered ones, and although they do sound good, I wasn't impressed with the performance of them at moderate to loud volumes. If these are going to act the same way, then I would say stay away from them if you do loud shows.
The issue that I am commenting on is the built in limiting. It was VERY annoying. When a loud part came up, you would definitely and very noticeably hear the limiters kick in, and then when the loud part was finished, the volume ramped back up again. I told the guy that he just didn't have enough rig for what he was doing, but it's what they got in the building and that's how it goes I guess.
Low to moderate levels and they'll sound good probably.
As for the Dynacords, I believe the power amp for the complete system is in the powersub315, then you just run wires from the sub to each main. The Powersub 315 can handle another passive sub hanging off of it also.
Here are specifications if you want to check it out more:
http://www.dynacord.com/en/products/7/2/19/7_powersub315.html
Here is the page with more complete systems available:
http://www.dynacord.com/en/products/7/2_index.html
And no, I'm not affiliated with either company, just submitting my 2 cents worth and some links to information for you to check out yourself!