The 2.1rc2 BIOS flasher crashes on your Quadra? That's a lot of no fun.

Do you have a NuBus PowerMac that you can try making the flash in?

I haven't actually used or owned a SE-IV for a few years now, but I still like them. Back when I had mine, I flashed it to 2.1rc2 using a PowerMac 8100.

Also, are you quite certain that you don't have a SE-IVD? The Differential SCSI version of the card uses High Voltage Differental SCSI and is incompatible with nearly all modern drives...