I've built two very quiet systems using a A-05B and a Lancool K7 cases. I'm about to put together a Ivy Bridge system that's going into a PC-6 case.
Since I don't game, I don't need a high powered graphics card. I do have 4670 passively cooled cards in the existing systems and the new one will use onboard graphics (an add in card won't help Lightroom, which is the primary use of the box). I generally don't like the way Lian Li manages the air flow in their cases. For cases like the PC-7 & 6, which are very similar, I would take out the front fan and only use the rear one and then tape over all the other openings on the rear panel and the vented slot covers. This way cool air comes into the case at the bottom of the front, passes over the drives, rises over the MB and exhausted at the top rear of the case. The air flow follows the natural convection currents in the case. If the openings in the rear aren't blocked, the air will be sucked in through them and "short circuit" straight to the exhaust fan and not contribute to the cooling.
As far as aluminum being a poor material for quiet computers, uh yeah.
The primary factor is the execution of the build details. The only issue I've had with cases contributing to noise are resonances of large panels (typically side panels). The simplest solution is to get some window/flashing membrane from a place like Lowes or Home Depot (http://www.homedepot.com/h_d1/N-5yc1v/R ... reId=10051
). It's a very sticky rubbery plastic that a couple of mm thick. It changes the Q
of the panel and works great.