This is proving to be a very strange design indeed! I've worked out a drawing, and it's so strange I had to keep re-checking it :o
.(Updated diagram shown above)
Cold checks with a meter suggest there are no faults, so the tone control should work, if there are no dried out caps, although with such low impedances I'm not quite sure how! The unmodified gain of the amplifers is 20, so those 1u feedback caps will behave as if they were about 20u.
Notice that DC supply to the microphones. This makes me think they are electrets
As soon as i can get into the office, I'll snaffle their all-singing cap tester and find out what the actual values are.
The 150n 'dry' caps are a guess based on the amp spec sheet.
The 0u22 ones are actually mis-printed so any dot would be off the edge of the cap. Size-wise they couldn't realistically be 22u, and it wouldn't make sense, bearing in mind the feed caps are only 33u.
All very strange :?