... he said that a bridged amp addressed the waveform a bit differently than an amp operating in stereo? And therefore, that imaging might naturally be affected, and thus a bridged set up might not be best for me after I assured him I was an old school, neurotic audiophile.Yes, bridged mode can certainly be expected to sound somewhat different than stereo mode. But the most predictable situation in which it "might not be best," for many bridged designs, would be if the speakers have impedances that are significantly less than 8 ohms, especially in the bass region (where lots of energy is typically required).
The reason for that is that in bridged mono mode a given speaker impedance will be "seen" by the output stage of each of the two amplifier channels as 1/2 of that impedance value. That is because for a given output voltage that is produced by each of the two output stages twice as much current will have to be supplied by each stage as in stereo configuration, since the "other side" of the load impedance (i.e., the speaker terminal that is connected to the other output stage) is being driven to an equal and opposite voltage by that other output stage. The voltage that is applied across the speaker terminals thereby being doubled.
So as is often the case for bridgeable amps the D-75a does not have a maximum power rating for 4 ohm loads when in bridged mode. A 4 ohm load would be "seen" as 2 ohms in bridged mode, which the amp presumably would not be able to handle with good results.
In any event, although I don't know what speakers you are driving with these amps, the fact that you are perceiving stronger and better bass would seem to bode well.
Happy Thanksgiving to you and yours as well!
Best regards,
-- Al