Benchmark AHB2 - To 'mono' or not to 'mono'

A lower damping factor will make the amp sound less tight and it may give you a slight bass bump at the speaker resonance frequency.

For the damping ot the membrane movement - speaker's own impedance is in the series with the amp's output.  Most of this impedance is resistive.  Assuming 6 ohm (for 8ohm speaker)  and 0.05ohm output impedance, we might have 6.1ohm vs 6.05ohm  - not audible IMHO. 

Electrical damping occurs because moving coil generates voltage that produces current in direction that causes motion of the membrane in opposite direction hence stopping the membrane.  This current is equal back EMF (voltage on the speaker) divided by impedance in the circuit that consists of amplifiers output impedance, cable impedance, and the driver itself.  At the end it comes to 6.1ohm vs 6.05ohm difference (about 1%).  Also for the same reason the highest effective damping that can be achieved is equal about 1.5 (nominal speaker's impedance divided by resistive part of this impedance).  It might explain why some tube amps, that have very low DF (as low as 1.5), still sound great.

There might be other reasons why some amplifiers sound worse when bridged. It might be unregulated (in most cases) power supply voltage that is sagging when twice the current is demanded.  AHB2 power supply is line and load regulated and should not sag.   From all the reviews, I've read, AHB2 sounded even better in bridged mode.