Number 8 uses a different injector model number, but that was to address a noise issue (probably most noticeable since that is the cylinder closest to the driver). I haven't heard of #8 failing any more or less than any other cylinder. #8 fails cylinder contribution tests a lot, but that is due to the CPS and is not caused by the injector.
If the injector is buzzing during the buzz test, I would replace the injector before I replaced the IDM. Injector failures greatly outnumber IDM failures, so much that you rarely hear about IDM failures. If you have the means to buzz test the injectors yourself, you could swap 2 injectors (put #8 in the #6 hole, put #6 in the #8 hole) and run the buzz test again. If the weak buzz moves to cylinder #6, you will prove it's the injector and not the IDM. If the weak noise stays with cylinder #8, it's an IDM problem (or wiring between the IDM and injector).