If the Corsair stock fans are too loud then 9/10 your MOBO isn't controlling them correctly and/or in addition you improperly installed the H100. I've read the 'reviews' but I happened to have gotten an H100 for free. The fans should be connected to the H100 internal controller, H100's (1) pin properly connected to the CPU_FAN header, and to a Molex 4-pin (2) used. The exhaust fan connected to the Exhaust_FAN header. Next the BIOS set properly i.e. Q-Fan and it's equivalent Enabled in the BIOS.
That said, I have my doubts the 'XSPC Rasa 750 RX240' kit will properly fit, the radiator is 124x63x280mm (WxDxH) then you need to add at least 25mm for the fans. Looking at the kit you'll need to make sure it has the mounting brackets you need (no MOBO listed).
Further, replacing the H100 fans with anything less than 90 CFM won't properly cool the CPU.