Why do you want low damping factor? The damping factor of an audio amplifier is unrelated to the slew rate or speed of the amplifier. An audio power amplifier's damping factor is defined as the ratio of the load impedance to the output impedance of the amplifier.
Loudspeakers have the tendancy to continue vibrating after the signal is gone due to inertia. Suppose the incoming signal is a "tight" kick drum with a short attack and decay. When the kick-drum signal stops, the speaker continues to vibrate so that nice, snappy kick drum turns into a boomy throb.
When the loudspeaker cone vibrates, it acts like a micro-phone, generating a signal from its voice coil. This signal generated by the speaker is called back EMF (back Electro Motive Force). It travels through the speaker cable back into the amplifier output, then returns to the speaker. Since back EMF is in opposite polarity with the speaker's motion, back EMF impedes or damps the speaker's ringing. The smaller the amp's output impedance, the greater is the effect of back EMF on the speaker's motion. An amplifier with low output impedance does not impede the back EMF, so the back EMF drives the loud-speaker with a relatively strong signal that works against the speaker's motion. When the speaker cone moves out, the back EMF pulls the speaker in, and vice versa. In short, the loudspeaker damps itself through the amplifier output circuitry. The lower the impedance of that output circuitry, the more the back EMF can control the speaker's ringing.
I would think you would want an amplifier with a higher damping factor. I am curious why you want one with a lower damping factor?
