Akrapovič p/n 63505979000, about £875. This muffler can be modified to remove the baffle by drilling one hole and unscrewing a screw. This is a picture of the necessary hole. Please note that the dimension of 32mm measured back from the end of the exhaust to centre of the necessary access hole to be drilled is not 100% correct. See this post for details. A plug can be bought from Akrapovič to close the hole, and it is referenced by KTM (P/n 76505099050), about €3.
Wings. Coober couples it with an ECU upgrade. 2300g, 1.35kg lighter than the original exhaust. Includes removable DBKiller and spark arrester. €630 with the rear heat shield included. Heel heat shield is extra, €52. It is smaller than the original or the Akra.
Rade garage works with Sharon and offers a Rally style exhaust requiring the removal of the catalyser . €330.
GPR have 31 different slip on you can order. And an optional decat pipe. GPR published a video showing some of these models mounted on a 790. Note this comment on this post by Raymond Wilson: “I have GPR on my 1290 Super Adv […] the GPR mounting system with the external collar that wraps round the pipe is crap. I see they’ve used this method on the 790 Adventure exhaust and this alone would deter me from ever buying one”.
SC project has multiple slip on available.
Remus also offers a specific 790 slip-on. €820. “Weight optimised”, not sure by how much. It’s quite nice in black…