One issues is just getting CD Burning software for the 68k machines. You could try Toast 4.x.x and see if that works. I had a USB CD-RW Iomega burner that came with a copy of Toast 4. I believe it worked under 68k machine too (FAT code)
The other thing to keep in mind is the data speed. the old hard drives in those machines could barely keep the data going at 1-2x, even if they were SCSI. I also think those particular SCSI Busses topped out around the 5MB/s mark, and because of the speed of the CPU/Bus, I would imagine it would be hard to read from a CD @ 2x (600KB/s) and pull it off in a steady stream without having to stop the flow to write to the hard drive, then re start the flow.
Those machines weren't very powerful, and a lot of issues early on in burning was the buffer under-flow where the machine couldn't get the data to the drive fast enough. I burned coasters all the time back in 1996 with my 4x CD-RW drive (which cost close to $1k IIRC which my dad scored from his business when he was laid off the first time) and that was on a pentium machine!
Plain and simple, the best way to burn is at 1-speed. it's probably the fastest you will get with an old machine.