OK, we know the printer and software works fine on a similar machine. Having a similar OS to test with is fortunate and ideal for troubleshooting like this.
That means that something is still messed up on your primary iMac. Multiple uninstalls and reinstalls have been tried with no success. Manual cleanup is unlikely since I am no expert on cleaning up the related files on a Mac.
At this point I would suggest reloading your iMac to bring it back to a clean slate. You would need your recovery CDs or a backup partition on the hard drive to complete that proceedure. Dropping the machine off at a tech shop to perform the data backup and OS reload shouldnt set you back too much either if you are not comfortable with performing it yourself.
Once the machine is reloaded you should be able to reinstall it like you did on your backup laptop to get it working again.
That, or you could retire the printer and go for a new one. Go with whatever is a better use of your time and money. it honestly might be cheaper and quicker to just retire the old printer than attempt to repair the OS.