I agree with Duke - amplifier damping is secondary to box and woofer selection...by a long way...it does not surprise me that pro drivers with underhung coils would sound tight as the woofer is always fully in control of the amp as Atmasphere describes (sees full force of the drive signal throughout its excursion and therefore behaves in a very linear fashion). Poorly controlled woofers with long coils in narrow gaps will be less well controlled no matter what amp they are connected to (as the coil moves in and out of the linear portion of the magnetic field they see less drive signal).
An under damped speaker may gain from a higher damping factor (10 or so), however a critically damped or over damped speaker is unlikely to benefit much from damping factor (it becomes a moot point as the mechanical behavior dominates).
However, a low damping factor (or high output impedance) coupled with a speaker with a large swing in impedance will certainly tend to emphasize the "peaks" in the speaker impedance response (often resonance for a woofer but a port can change this).
When under damped speakers have a typical bass hump in frequency and also have a high impedance at their resonance then a low damping factor amp will almost certainly give you bass bloom as both factors discussed above may combine to give much stronger bass.
