My friend, from what I can paste together you are asking about if you can set up the Poseidon's in parallel or serial water cooling? The answer is yes to both. You can set it up for parallel OR serial.
[Image from EKWB Installation document]
Now, I'm not sure if you 'like the idea' or 'dislike the idea' of the Poseidon design or not. The new GM204 GPUs are very efficient, and currently I have the Strix GTX 980s which, if I'm not mistaken is the same PCB as the Poseidon GTX 980 (ASUS employee please correct me if I'm wrong). They never get any hotter than ~65C when I game. I don't believe that the difference will be great between the full cover water block for the Strix and the Poseidon cards in regards to GPU temperatures. If you want bang for your buck and you're new to water cooling and don't want to void warranties - get the Poseidon's. Or, if you want a full water block, the other option for a factory installed water block is from EVGA and their HydroCopper series.
I hope this helps you, I believe you used some sort of translator application in your message.
ASUS RAMPAGE IV BLACK EDITION | INTEL i7 4930K | G.SKILLZ RIPJAW X 32GB | ASUS STRIX GTX 980 TWO-WAY SLI | CUSTOM WATER COOLING
RIP