SOLVED!
Took awhile, though. I had to upgrade BIOS directly on that card (it was stone-old), and it worked - almost instantly! No hangs at all any more. 5.4.xx
works perfectly (was 5.0.xx). Even that aforementioned Samsung 750GB drive now works like never before.
The update tool is called UPDFLASH.EXE
. Updating worked great even in DR-DOS
booted via grub
. (Not going to mess with floppy disks ever again, that one is for sure.)