Hi Hans,
I'm sorry, I don't know how to build it. 
I've tried, in the mean time, to boot it with freeBSD, and it boots and can see the disks, but it uses mr_sas as driver I'd say. 
Could it be that freeBSD's mr_sar has this status ?

In any case, if you can build me an ISO it would be great.
Thanks.
Maurilio.