Without modifying the synoinfo.conf file I actually only get 6 disks visible in the storage manager with a default install. See attached photo.
I achieved 10 drives by modifying both synoinfo.conf files. I modified max drives, and the 3 hex fields for internal, usb and esata,
The 2 HBAs are identical allowing for 8 drives per HBA. I have a super micro motherboard and have disabled the onboard sata ports.
The HBAs are IT Mode Genuine LSI 9211-8i SAS SATA 8-port PCI-E Card.
I also tried to append SataPortMap=22 and get 10 drives. Trying SataPortMap=12 got me to 11 drives, but I can't get to 12 drives.