No need to buy heatsink for TY-100, you can order TY-100 directly from Thermalright, just contact them
It is slightly more noisy than the Noctua but it's not too bad
You can't get the NF-A9x14 2.5W version without buying the whole NH-L9i cooler.
You can get TY-100 alone by contacting Thermalright.
NF-A9x14 2.5 is the best compromise between noise and cooling performance imo
Are you sure you used the 2.5W version of the NF-A9x14 and not the 1.4W version of NF-A9x14? The 2.5W version comes bundled with Noctua NH-L9i and spins faster. The 1.4W version comes when you buy the fan retail
In my testing on a core i7 6850K OC'd to 3.9Ghz and stressed with AIDA64...
It was my original idea to cram a 92mm slim fan below the mobo.
Honestly, just take the riser off the case, it's just 2 simple screws. Fit it back in when you are done installing the fan. Are people seriously trying to cram in a fan with the rise cable on? *facepalm*