I've used SCIOCCOMMAND successfully to read CDDA frames from a SCSI2
CDROM drive using the scsi stuff in -current on an i386.  CDDA frames
are 2 channel, 16bit 44.1kHz samples with 1/75 second per block, for a
total of 2352 bytes per block.  No sane buffer cache can handle that
directly, so I use SCIOCCOMMAND to issue READ(6) commands.

I've also done mode sense and mode select on a SCSI2 tape drive using
SCIOCCOMMAND.

==John