S2600CP, problems using all 8 Blue SAS/SATA ports in SATA mode

I have a S2600CP board (latest firmware, 2.05.004) in a Intel P4308XXMHGC Case.

There are 6 WD 600GB VelociRaptor *SATA* drives in the two Hotswap Disk enclosures, They are connected via two MiniSAS->4 SATA cables to the 8 Blue SATA/SAS ports.

Op.Sys. I Proxmox 3.4 (Debian Wheezy), kernel 3.10

The first four drives are correctly detected and usable, but the next two drives, which are on Blue ports 5 & 6 are not seen at all. Have tried all controller modes (RSTe, ESRT2).

It was my understanding that in SATA mode all 8 ports were available

Have put in a C600 upgrade key (RKSATA8) but that made no difference. However the BIOS showed no Comtroller Modules installed, so maybe there is a problem there.

Any suggestions?

thanks - Lindsay.

Edited: Corrected MB Model typo