I haven't done bars but I've done carbon cranks, a seatpost and bottle cages before.
I used wet sandpaper from the automotive section of a hardware store. Started with 400 until the logos were gone (can take a while) then used 600, 800 and 1500 to even even things out. Then I wiped them down and cleaned with some solvent before spraying some automotive clearcoat from a can. I sprayed it on thin and did a couple coats. Once you've done that you can use the 1500 grit to wet sand the clearcoat for a matte look.