LOL, sorry.
I am trying to point out RAM which won't require you to do any fancy changes in your BIOS. And remember that any changes you make to the BIOS - other than failing attempts to update it - can be undone in a few seconds by clearing the CMOS - the thing that saves changes to the BIOS.
Let's compare the 4 RAM slots in your motherboard to 4 light bulbs in a simple bathroom light fixture above the sink! Right now, you have two bulbs in the row and you get pretty good light from it. The light is even because both bulbs are the same wattage and brightness. But you'd like more light to see by at the mirror. So you add a couple of new bulbs. Well, these new ones are actually a higher wattage and they make the new brighter light uneven. This is annoying - but at least you have brighter light. You can avoid the problem by getting new bulbs that match the old ones properly, at least being the right wattage. They might not match perfectly and have a tiny bit of difference from the old bulbs - but it's much better. You now have brighter and even light. (The only way to get perfect light is to get 4 new bulbs, a greater expense and poor choice.)
So... we want the same voltage on your RAM because many people have problems using 2 modules of one voltage and 2 modules of another voltage. I think all RAM should be 1.8V but I'm not making the rules. Normal DDR2 modules require anywhere from 1.8V to 2.3V to operate. There are settings in the BIOS of newer motherboards to adjust this voltage to get the proper "light" out of the RAM. Since your currect modules want 1.9V to 2.1V, we'd like to make sure your new modules are similar.
I don't know whether your BIOS is currently giving the old RAM the voltage it really wants! But the best way to make sure the new RAM works, is to buy modules like the ones you have - that's what I recommended above.
Why does some RAM use more voltage? You may have noticed that the folks who talk about "overclocking" their computers often talk about giving the parts more voltage. Generally, a tiny bit more voltage delivered to an electric device makes it run faster - or makes it able to run faster. Give it too much voltage and it burns up or wears out faster. The RAM manufacturers are basically doing this. In order to make their RAM faster, they take modules really designed for 1.8V and tell the user to give them a little bit more in order to achieve faster/better performance. If you don't give 1066MHz RAM that says it wants 2.1V all that voltage, then it drops down and works like 800 RAM.
Anytime you have a lot of devices in a row there's a loss of efficiency. So that 4 modules may require a bit more Umph of voltage than 2 modules.
----------------
Ignore everything explained above if you want. You came and asked for advice in selecting some new RAM for your system. I gave you very specific advice on what to get to be sure it worked. Take the advice and I'm sure you'll be happy!!!