[Richard Crowley]

Mike Rivers wrote:
Not exactly. I don't have the schematic, but it's not just resistors
and it's not a tapped transformer. There are a bunch of inductors and
capacitors on the circuit board in an area associated with those two
channels that aren't in the other channels. I think they're "faking"
it. G But it definitely makes a difference.

In addition to whatever it does in terms of loading the mic, the low
frequency rolloff changes as you change the impedance setting. At the
2.4K setting it's flat down to 10 Hz. At 500 ohms, it's down about 2
dB at 20 Hz, and it's about 4 dB down at 20 Hz at the 300 ohm
setting.

Almost sounds like the extra loading was applied AFTER the
phantom-power decoupling capacitors (thereby effectively
forming a high-pass filter).