7.5.5 on 8600 - enabler?

Apple spec says 7.5.5 with Enabler 702:

http://docs.info.apple.com/article.html?artnum=112397

Hey, ubp,
Your SCSI scanner is what brand? If it is Apple, that is a known issue with OS8 and later. Get the "new" driver from http://www.info.apple.com/support/oldersoftwarelist.html
They have it well hidden as "Macintosh/Display-Peripheral/Scanner/Dispatcher-Ofoto Drvr4.2.sea.bin"
Also, you may need virtual memory turned on when the scanner is attached. With the updated driver and VM on, it should work fine with OS 9.1. But you may have some other issue with OS9.1 because it is never way to slow for me. What? It's not an Apple scanner? Never mind...

upbeatpenguin
The 7.5.5 on oldersoftwarelist is only an update from 7.5.3-you will need that first! For the 8600/300 with OS 7.6.1 no enabler is needed according to specs.
IF you download on PC you should download all files of 7.5.3 in one folder,burn this folder to a CD(slow speed,ISO 9660),transport to the MAC,copy the files to desktop in one folder,use Stuffit to expand. You also can try to connect via Ethernet and transport folder this way from another Mac(don't expand on that MAC).

With a cool old Mac like an 8600 which can do so much, it would seem a shame to downgrade the operating system, especially to a pre-OS 8.1 system which cannot do the HFS+ file system.

As someone else suggested, I think your speed issues are being caused by something other than OS 9.x. I have a slower Mac than yours and I see no appreciable speed difference to when it is booted into OS 8.6 as opposed to 9.1. I also have three widely different SCSI scanners, all three of which work plug 'n' play. The speed issue of the scans is a function of the scanner hardware, not my operating system.

upbeatpenguin
According to EveryMac, the lowest OS supported by the 8600/300 as it was released was 7.6.1. You might be able to refocus the Mac's thoughts towards 7.5.x with WishIWere, but that seems to be more like punishing the Mac than enabling it.

As others have suggested, the preferable path should rather be to attack the peripheral hardware that you wish to use. You need to take account of the HFS/HFS+ difference in CD burning, and the different characteristics (from current production) of older CD media. Your burning app will control much of this. For example, if you are not offered HFS+ the choice does not have to be made. Available (SCSI) data transfer rates will also have an effect, but test (simulated) burns will tell you about any deficiencies in rates. OS 9 is far and away the preferable environment for burning if you have supported software, and an updated driver for the burner. Similar considerations will apply to scanning. Be aware also that there can be possible (but solvable) conflicts between peripheral drivers/software and native Apple extensions.

PS. All of this assumes that you are not simply in the grip of inadequate RAM for the 8600.

upbeatpenguin
One quick notion for you to consider. Without too much travail you could maintain the 8600 as dual-boot (OSs 7.6.1 and 9.1). A small (2-4GB) second HDD, formatted HFS+ and containing 9.1 and supported software, could ease the exercise. Then you could use the latest (and most versatile) software to control burners and burning in OS 9.1, and easily revert to the HFS-formatted HDD and 7.6.1 when you pleased.

There is a severe limitation to having a local extended format volume (drive) when you are booted to OS 8.0 or earlier (sych as 7.6.1). You cannot see any files or use any applications on the extended volume except one file that says "Where have all my files gone?".