Hard to diagnose squeaking
One thing you haven't mentioned: when does the noise occur relative to crank position? Does it make the noise through the entire revolution of the crank arm? Is the noise loudest at a certain point in the crank revolution (say 2 o'clock)? I had a customer come in one time with a sound they absolutely could not get rid of and they went through most of the steps you mentioned. Turned out is was one of the chainring bolts. A little grease on the threads and the problem was gone. It was a ridiculously easy fix for a ridiculously maddening problem!! May not fix your problem but it only takes a couple of minutes to try this solution. You should make sure that all threaded surfaces have grease or anti-seize compound on them. Bare metal threading into bare metal is no-no as it leads to annoying noises, bolts coming loose or bolts seizing/corroding. Good luck!