Actually, the 'controller' (rather host bus adapter HBA) is just a SCSI device like any other.
(There's no 'bus master' in SCSI unlike IDE, USB, ... There's 'targets' and 'initiators' but these are just temporary roles that can change at times.)
If you look at it that way, you connect your wide devices (HDDs) with a wide cable, terminate properly, and adapt your narrow device (HBA) - that's it.
It's getting more complicated when you're building a SCSI bus that's wide for the first part (HBA, HDDs) and then gets adapted to narrow to connect older devices (CDROM, scanner). Then you'd need to use a 'half terminator' to terminate the upper byte while going narrow. Once I used a shared bus with an Adaptec 2940W at one end and my A3000 at the other with half termination in between. But no need to get more complicated here.
