The R7 thing may be an even more of an issue than it seems. The buf634 / lme49600 datasheets mention the situation of the buffer output not following the input, and hence the input-output clamp diodes turning on hard, can happen if the buffer output is shorted (while the op amp drive continues on the buffer input).
I just realized that situation can easily happen if the buffer chip's output is going through a typical TRS jack. They all short momentarily when the TRS plug is inserted or removed. The buffer chip would survive due to the internal current limit, but the op amp might be wiped out without a large enough R7 to limit the buffer input current due to the input clamp diodes turning on.
My math in the previous post forgot the 3V clamp diode drop inside the buffer chip. With the drive op amp's output up at a 12V rail and the buffer output shorted by a TRS plug insert, the input current through the buffer input clamp diodes would be (12V - 3V) / (750 + 200) = 9.5mA, or 12.3mA with +/-15V rails, or 15.8mA with +/-18V power rails (with an additional 750R buffer input series resistor added).
I just realized that situation can easily happen if the buffer chip's output is going through a typical TRS jack. They all short momentarily when the TRS plug is inserted or removed. The buffer chip would survive due to the internal current limit, but the op amp might be wiped out without a large enough R7 to limit the buffer input current due to the input clamp diodes turning on.
My math in the previous post forgot the 3V clamp diode drop inside the buffer chip. With the drive op amp's output up at a 12V rail and the buffer output shorted by a TRS plug insert, the input current through the buffer input clamp diodes would be (12V - 3V) / (750 + 200) = 9.5mA, or 12.3mA with +/-15V rails, or 15.8mA with +/-18V power rails (with an additional 750R buffer input series resistor added).