I have gotten lots of adaptec 71605 cards from ebay with 7.6 32136 FW in them.
I think the 7.6 firmware is for NetApp Only .
Using MSM or the Adaptec BootableUSB I updated them to 7.5 32118
If it is in cache preserve mode I use the above BootableUSB or I put the slot in EFI Mode in the computer BIOS
https://storage.microsemi.com/en-us/speed/raid/storage_manager/adaptec_bootusb_v3_07_23980_zip.php
ARCCONF PRESERVECACHE 1 CLEAR LOGICALDRIVE ALL
ARCCONF PRESERVECACHE 1 DISABLE
Then I use the MSM to put the FW back to 7.5