wow... that was a lotta reading.
I know how frustrating it can be. I almost quit brewing about a year and a half ago because I was getting an off-flavor on my new rig that I couldn't find (and I still get a ton of crap about it from my dear "friends"!!!) It is insanely frustrating though.
I dunno... my two cents is on the only thing I haven't seen anyone mention (maybe I missed it) is your kegs. Are you occasionally completely breaking down your kegs (removing dip-tubes, removed o-rings, etc) and giving them a good cleaning... and THEN a good SANITIZING? (cleaning and sanitizing aren't the same thing). It is really easy to get a bug in a keg and I think a basic infection will toss off all sorts of off-flavors.
I think your current hefe might be a good test case... if it tastes ok now... give it another couple weeks and see if it still tastes ok. If it does... it's probably not a keg issue. If it doesn't... then you may have found your culprit.
Good luck though... trust me, once you find it, it's going to be awesome to brew again.