Nicola,
I can't give you any advice specific to your hardware but I am testing 8b6 on a new Gigabyte motherboard with 2 SATA controllers, ports 0-3 and ports 4-5. I have my two disks on ports 0 and 1 and the CD on port 4.
Initially I had both controllers set to AHCI and the installation went well. When I tried to re-install over the old installation the CD was not recognised until I changed the second controller to IDE mode and everything has worked well since then. Hope that helps.
Lloyd.