29x2.6 is max on the rear.....no chance for 2.8
for 27.5 a 2.8 would fit...but take a look in your manual. the max tire sizes are listed there.
In manual 27.5x3.0 are max
you have to remove the CPS washers under the caliper! you need these washers only when you have CPS calipers like SRAM Guide RE!
then you can use your QM44 for front and rear for the 203mm rotors