With this much complexity and so many semiconductor junctions in the signal path - why bother with the extra complexity of a differential tube front end?
kenpeter said:What is the purpose of C3 & C6 1000uF?
Are you bootstrapping here to widen the effective rail?
Beware of amplifiers driving capacitive loads....
As I see no global feedback loop, it might be alright.
Depending how you were planning to servo out
the bridge, that capacitance might yet become a
feedback loop problem...