I believe you're right about the insert. I thought it was 6dB down. I knew one engineer that brought his tape returns back on the insert returns to get the extra 6dB and grind the board a bit. You need to use the VCA groups for everything though, depending on the vintage of desk, as some cut only at the input.
The actual bus or direct out amp is on the group amp (294) card, and is a perfectly cromulent line driver. Lower right corner of the schematic. You need to strap the input switching fets low or high, depending.
