If you don't need RAID function, maybe you can go for a SAS module AXX4SASMOD. See Spares / Parts list and configuration guide.
RS2WC080 supports JBOD fundtion, means drives not configured as part of a RAID array can be configured as “pass through” drives in Non-RAID mode. RS2WC080 supports S5520UR board, however it hasn't been tested in the SR2612UR system. So you'll need to test it on your own if you want to.
The SR2612URR has active midplane - LSI expander.
See picture here:
Means you can use RS2WC040 or any other 4port card and save money. 8port won't help anyway.