Hmm. Well, this technique is best referred to as "sneakernet": the drive can only hook up to either the D824 or your PC thing one at a time- not both. Both are SCSI bus masters, and the SCSI drives can only talk to a single master at a time. So there is no way to plug a drive into both at once.
I frankly don't know a thing about setting up a SCSI adapter on a pc- I don't use them as yet, being a UNIX guy with native SCSI-based systems. You'll need to query some of the PC-based folks for that one. I'm sure that it will involve getting a PCI SCSI adapter up and running. However, once you do get that set up, you can format your external drive using DOS format commands with the old DOS FAT16 filesystem. This is all the 824 understands for .WAV export: the old filesystem with a max of 2 Gb.
When you're done with that, you can power everything down (SCSI is _not_ a hot-swap technology!), unplug the drive from the PC, carry it over to your D824, plug it in, power everything back up, and use the utility menu to write .WAV files to the DOS-formatted drive. The D824 "format" command *cannot* do DOS formatting. It can only do Fostex FDMS3 formatting, which is completely proprietary and useless to anyone but a Fostex box (but semi-convenient for backups). For .WAV export, all formatting must be done on the PC...
When you're done with writing the .WAV files on the DOS-formatted disk, you can power everything down, unplug the drive from the D824, carry it over to your PC, plug it in, power everything back up, and access the .WAV files.
Sneakernet. This basically rots. My take on this is that it is vastly preferable to have a pair of Jaz drives that remain permanently connected, and just carry the media (which *is* hotswappable!), rather than drag an actual hard drive back and forth. In my experience, SCSI cables do not like continual plugging and unplugging, so hard-drive sneakernet is a failure waiting to happen.
The speed of the SCSI-II adapter is pretty much a nonissue. SCSI-II is 10Mb/sec, and that's it- and the D824 and the removable-media drives can't go that fast anyway. Dumps to SCSI on my machine actually do not appear to be significantly faster than real time. Which is why the DAW I've been trying not to build will have 16 channels of ADAT in/out, so that I can just ship the data over optically from my D1624 (at real-time speeds) to the DAW (and vice-versa) and avoid the whole sneakernet hassle altogether...
I'm not a big fan of Fostex's SCSI implementation: it is clearly an afterthought, and a kluge at that.
Hope that helps.