Im using a Korg D1600 at the moment and it loves SCSI extras. It wont run unless there is an internal HDD installed as that’s where it keeps its OS however I don’t know if the Fostex works the same way or uses ROM chips.

I looked round the back of mine, located the SCSI port, confirmed it was a 25 pin interfaces and got a redundant external hard drive from work (I did ask first !!!!)
As SCSI tech is quite old, if you have the interface, you may be able to pick up an external HDD very cheaply and use that (you may have to format the drive) instead of shelling out for a new internal IDE drive.

Best of luck
S