The akai sampler itself is terminated.
You can use the internal SCSI connector and external SCSI connector at the same time (at least I do.)
I have build in a Iomega zip drive, which is connected to the internal SCSI connector (termination set to "off")
At the same time I have an external SCSI CD-rom player and an external SCSF CF reader connected. The last external SCSI device is set to termination on.with a termination block
Please be aware that you must put the SCSI connector of the SCSI flatcable "the wrong way around" in the SCSI connector of the Akai SCSI board. (at least with my S1100 and most other Akai S samplers)
Cheers