This achievement is awarded for using any Marshall gear when creating a tone in "Tone Designer" from the main menu.
Select "Tone Designer" and then "Edit tone".
Select Amp and then use the change option at the bottom of the screen.
Now select any Marshall amp, I personally used the "JCM800"
Now you can couple this with another achievement and get 2 together.
Now select the Cabinet and change it to either an Orange or Eden cabinet. Any model is fine and you should also get the following cheevo.
Or