Personally if your watercooling you CPU and GPU the northbridge would be easy enough to add in unless its heatpiped to voltage regs and southbridge in which case you will need to get some more water blocks or get some air cooling for these items. Thermalright offer good Mosfet coolers.
Case wise it really all depends on how much modding you would be happy doing? The Akasa Omega could be made into a really amazing watercooled case with no modding you could fit a duel and a single rad and with a bit of imagnation I think you could potentially get a quad in the top after moving the PSU
Antec 1200 would fit a triple in the front you would just need to find somewhere to put the hard drives.
If you fancy something a bit different then the Thermaltake Mozart TX could be right up your street will easily accomodate 2 duel rads.