Here's where this stands right now:

The only way I can get the Apple Cinema Display 20" ADC to work with the 450MHz Cube is when I boot the Apple Hardware Test CD.

It's odd that the official Apple Cube Software Install CD boot-up doesn't work with the Cinema connected, but it works with a Samsung LCD display connected.

When I boot the Software Install CD with the Samsung display connected, which is OS9, the internal disk (which is the stock 20GB hard drive with MOS installed) doesn't show up. Not in Drive Setup or Drive First Aid programs. Does being formatted for MOS cause OS9 to not be able to see it?

All tests pass under the Apple Hardware Test. As far as I can tell, that does not test the disk drive. However, I was able to install MOS a couple of weeks ago and prior to that I was running NetBSD. I think the disk drive is okay. MOS looks good on the Cube with the Samsung display connected.

The current firmware showing in the Hardware Tests profile tab is 4.1.3f2. I don't have any way of updating this without being able to install OS9 on the disk.