all i can reccommend is not to get the zalman reservator 1v2 or 1 unless you're planning to fit it with a fan (for an extra £20, 40USD) these systems work on the abient air temp to cool your computer.
im not sure about adding another radiator, im not sure if the system would handle it at all well, nor what sort of impact it would have.
the best thing you could do is buy another radiator and try it. report back to us your findings (but don't blame me if your pc blows up)