A Question Regarding RAM...

You only 'regain' dual channeling if the memory architecture of the specific model Mac supported it in the first place & the specifications of the RAM DIMMs themselves match the RAM specifications for the system they are being put into.

Performance differences between 6GB & 8GB RAM will only manifest themselves if your system is actually using all that RAM in the first place. To be honest, this is not likely. There aren't many apps that can use that much RAM. Photoshop CS can; Aperture can. Office apps, browsers, iPhoto, Final Cut and most other apps generally can't use more than about 2-4GB RAM.

As long as the RAM works, you should be fine. However the risk is that if you insert RAM that doesn't match Apple's RAM specs for the model Mac you have, you risk frying either the RAM or the logic board or both. Consider yourself lucky that your 2GHz MBP only failed to boot and didn't end up dead.

Computer manufacturers specify the max RAM based on their design specifications for each product; it is not based on a nebulous "what is available at the time of manufacture". There are many factors that contribute to the amount of RAM a particular computer (motherboard/logic board) can support.

Simple

1: Use MacTracker to find out the exact amount of RAM your machine can handle.

2: Use Crucial.com checker, punch in your machine and the RAM upgrade most likely used and grab the specs or order it there.

Do not mess around, touch the contacts, discharge static onto the modules or electronics etc.

Use a catch mat and a plastic compartmentalized holder to place each screw/part in order of disassembly so it's reassembled exactly the same way, some screws are longer or of a different thread than others on Mac's.

Use the right tools and follow online pictures and instructions.

The more you mess around and experiment the more reason for something seriously wrong to occur to the hardware and then your out of several thousand dollars of equipment.

It's far better to let your fingers do the walking and your mouse clicking to learn than it is to take a chance on installing the wrong component into the wrong machine.

If you match the pins "200 - DDR2", and frequency "667Mhz", why would the amount increase damage the logicboard ?

It's not about the amount of memory. I didn't say that. What I said was about matching the Apple specs for the specific machine. The frequency is important, yes, but equally if not more imporant are more arcane hardware characteristics such as buffering, ECC vs non-ECC, single vs dual channel support, timings, CAS latency, etc. and frankly the quality of the RAM itself; and whether or not the RAM characteristics match what the system (memory controller, memory bus) was designed to support.

While in the US I can plug into the walls 120V socket and charge, or run the computer. Likewise, while in the EU without fret, the adapter regulates to work up to 240V...

That's because the power adapters were specifically designed to support those two voltages.

Would you even consider plugging into 480 VAC in order to get more power? Would you even think for one minute that the system would run if you plugged the adapter into a 24v DC supply? I don't think so. You know it wouldn't work because the voltage or the type of power is beyond the capacity of the adapter to handle it. Well, similar principles apply to RAM as well. The system is designed to support RAM that meets certain specifications. RAM that doesn't meet the specs may or may not work at all; may or may not work reliably; or may or may not damage the system. Depends on the degree of mismatch between the characteristics of the RAM and what the system was designed to support.

I'll just stand by what I said at the end ... so far you have been lucky.