How much do you want to spend? I assume you're looking to watercool the GPU,CPU ? Anything else? You could watercool the motherboard aswell but personally I dont see the need to.
How long do you plan to keep you gtx560s? If you plan to keep them for a short while (less than a year or 2) I would suggest getting universal GPU blocks which work with most GPUs that way when you upgrade you can take them with you! Ek Supremacy is the successor to the EK Supreme
HF VGA which is very good, can be had for <£40 then grab some ram, vrm sinks which will set you back around £5 for each set so you're looking at £50 per gpu.
for the cpu I assume its an i5 2500k, pretty low power and the gtx560s what clocks do you have them running at? I would say a 360mm rad is enough something like the XSPC RX360.
What do you want from watercooling? High overclocking performance or silence? If you want silence then i would recommend the RX360 radiator as its the best performer with low rpm fans (still great with high rpm fans), for pure performance then something like the Hardware Labs Black Ice® GT Xtreme will be better. Skinneelabs is a great place for information
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I believe your case supports a 360mm radiator at the top so should be ok
. If the Rx360 is to thick then there is the new XSPC AX360 which is the best slimline radiator out (almost matches the RX i think).
Ill hopefully make a more concise post when you post back a few more details
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