Well, I'm a bit of a johnny come-lately to this thread, but here goes.
First, while naquadria can be derived from naquada, I THINK that it's been stated by Carter or someone as being another element. If that's the case, it's likely that it's derived from Naquada in much the same way as Plutonium is derived from Uranium.
This would especially make sense since you have weapons grade naquada. Using uranium as an example, uranium naturally occurs with different isotopes mixed together. Most of it is plain U-238 with a small amount of U-235 (approximately .7%). To make weapons grade Uranium, you have to seperate the two to increase the percentage of U-235. Weapon's grade uranium is typically about 80-85% U-235. It seems probable that naquada is similar and one of the isotopes is more unstable and thus fissionable.
Trinium is NOT a superheavy element. It's apparently just something the producers pulled out of thin air. It's been stated that it's superlight and superstrong.
Um, crap, I think there was some other stuff too but I forget what now. That's the most of it though.