Wow, that's a pretty good setup you've got! I can see why you want to dump the USB/FireWire card...

All I can say is that you should give it a try. A brief look around the web doesn't find any Macintosh specific information, but it seems that the SCSI PC Card reader devices for Windows are all recognized as removable drives, so I would assume the same is true for the Mac. This indicates to me that the cards themselves should be hot-swappable.

I have no personal experience with this. Maybe someone else passing through does...

Good luck!
Peace,
Drew
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Power to the PowerPC!