Which bus drivers to include when compiling freeBSD kernel?

I'm trying to compile a FreeBSD kernel and make it as light as possible. I'm struggling with the configurations on the bus, especially the SCSI Controllers part. there are many modules e.g: ahc, ahd , ... and I don't know how to find out which ones I need.When I run dmesg I get two entries for buses:

1. ACPI PCI Bus


2. ISA Bus

But I also get something about SCSI in :

cd0: Removable CD-ROM SCSI-0 device

I'm Running FreeBSD 9.3.0 on a VirtualBox VM on an i686 pc.

should I keep the SCSI Controller Modules? If yes then which ones?