I am making a Extreme Build and it needs 1643 watts i they dont have 1700 watt power supplys
Just use two psu's which I'm guessing you can since you are doing a extreme build, it should have a extreme case, or go for the Superflower one Radox mentioned.
If it's that "Speed Build", you probably have some issues aside from the PSU...
If you get two PSUs, you have to do a bit of extra work to get them to work together, as I believe you need a motherboard signal to turn the PSU on (like the paperclip test). I remember hearing about a specific adapter that would trigger it, bit can't remember where (or when) I saw it.
phanteks has a dual psu adapter for the mini XL case. you're right, this build is messy and not thought out. for starters, the case doesn't have mounting locations for all those radiators. the three video cards take up all 6 pci-express slots, so there's nowhere to put the sound card. wouldn't take the BX 100's for a workstation.
what the others said, except since your doing an extreme build, I would get a caselabs or 900D to fit the Titan X coolers, and H100i,s (which suck, use like kraken x41's or something, im not sure they perform as good but theyll be quieter and wont take up as much space).
i look into these