I'll start by saying that I built a 7.56 kg disc bike using a 1000 gram frame, 400 gram fork, and 400 gram rims. Campy Chorus mechanical, TRP HY/RD calipers, Shimano RT99 rotors, and pretty nice finishing kit including a Fizik Arione R1 and Ritchey Superlogic seatpost. You are trying to remove ~2kg from the weight of my bike which won't be all that easy.
To have any chance of getting sub-6kg, you'll need to start with far lighter rims than 400 gram clinchers. There are 250 gram tubular rims that could be built with Tune or Extralite hubs and 20F/24R CX Ray spokes to shave ~450 grams from my build. You could run SRAM Red mechanical and Juintech calipers with Ashima rotors (don't bother with the junk carbon rotors, I've never read a single good thing about them) and save another good chunk of weight. The rest of your build kit will save some more weight, too, but I'd need to see it all in a spreadsheet to know just how much.
For thru axles, I'd suggest Carbon Ti X-lock which are a little bit lighter than standard fare flush thru axles. I couldn't justify the price but this build doesn't seem to be as sensitive to price as mine.
Use the lightest cable housing you can find, consider an aluminum cassette, and stick with narrow tires and possibly you can get close to your target weight.