I have received further information when I suggested I was to post the info on the Forum
Question - 1149579
From : Derek GC White [ derek.white@whatispossible.co.uk ]
Sent : 11/3/2011 17:30
Question : I would like to clearly understand this answer so I can post the answer on the Forum
Although all the documentation and publicity for the GA-Z69XP-UD3 board clearly states there is both an Intel & Marvell RAID controller you are saying it is not possible to use both at the same time

Answer : Hi,

If,

- Set up either Marvell GSATA or Intel SATA in Raid mode with no problem.
- There may be no raid configuration option appeared in POST when both controllers are set in Raid mode.
There is shadow ram limitation as a general answer in public after confirming with bios engineers.
The shadow memory is fixed, so that there may be not enough shadow memory for raid controllers.

This is interesting if you refer to the Wiki entry
Shadow memory - Wikipedia, the free encyclopedia
Which suggests there are efficient and inefficient ways to organise memory - I am sure that applies to BIOS as well

To disable one of the other is a way to get enough shadow memory for the configuration.