Hi
The C9.25 CF XLT should ship with the (wider) CGE dovetail mounting rail, not the (narrower) Vixen one. Therefore, your mount will require a Losmandy style saddle plate to accept the 4” wide (3” dovetail) rail.
There are also mounting holes on the top of the corrector cell and rear mirror cell. I believe that Losmandy sells a mounting plate for the C9.25 - see here:
http://www.losmandy.com/secondary.html#DC
Then, you add Losmandy rings and that should do the job.
WARNING – Losmandy are expensive.
Cheers
Dennis