The excellent Monitor Audio RS6 / RS8 can be effectively upgraded by replacing the tweeter with the Morel Elite Series ET448:
The ET448 is a very sweet and smooth sounding tweeter with the added benefit of a replaceable dome / voice coil assembly.
This is a straight forward replacement requiring minimal work. Other Monitor Audio speakers of the same era using the far eastern Gold CAM tweeter can also benefit from this modification.
Click on the images for full details of this tweeter.
Full details of Morel Loudspeaker Technologies below:
Willys-Hifi Ltd - the specialist UK loudspeaker parts company