So, wanted to update this thread with the recent modifications to the schematic. Basically, this consists of running a resistor from B- to the input stage tail current source, and changing the top MOSFET in that current source from a DN2540 to a 10M90S, which increases its voltage limit. This should protect this current source from frying if one of the input tubes goes bad. With this change, C- in the power supply is no longer needed, so the only connections from the power supply are B+. B- and ground.