Thanks again Dave,
Will try that tomorrow, and will also try swapping the two M.2 drives as I mentioned..
Have swapped the two M.2 SSD drives on the DIMM.2 and arranged the BIOS to DIMM.2_1 + PCIEX16_2 in the CPU PCIE Configuration Mode and as I thought, now both the INTEL 1.2TB drive and the M.2 SSD are present and selected to boot from the M.2 drive.... I have thus been able to format the INTEL 750 and have an extra 1.2 TB to use for games & programs.
One problem though... The second M.2 ssd drive is gone !! I will place it in a normal M.2 slot on the MoBo and go from there. (but no idea why this second M.2 drive on the DIMM.2 is not acccessible...).
Just purchased a faster GTX 1080 Ti GPU, so I have no intention of reducing the GPU performance, so I will leave it as is for the time being.
Thanks again and best regards,