[jcp123]

Hmm lots of directions to go. Do you have an SGII or similar instrumentation? Something with some live data would be good. Misfire counters can be fooled.

You can do a quick and dirty cylinder contribution test by unplugging your injectors one by one. Similar to the cranking sound test you did, listening to the rpm drop with each injector could help you narrow it down.

Since you say it feels uniform from idle to redline, I don't think you'll find anything here, but you might take a spray bottle with water and spray around the intake, listening for a change in idle quality and/or if any water is being sucked in. For good measure, spray anywhere there might be engine vacuum.

Don't forget a basic visual check: look for anywhere wiring might be compromised, and if your car has a mass air sensor, pull it and see what the elements inside look like.