In my experience a lower damping factor usually means more bass because the cone moves more (higher x-max at resonance). It is not until the power exceeds the compliance of the speakers' suspension that the lack of damping is ever a problem. Once the power level is at that point for a given speaker driver in a given box or baffle, then having a damping factor greater than zero will allow the speaker to play louder without distortion. So if the speaker has to be played loud to too have bass, then some damping would be desirable. If not, then damping will result in less bass.
The SE34I.5 is a triode wired pentode(EL34) or beam tetrode (6L6) amplifier that by being wired as triodes have linear output into all impedances making the damping greater than zero. The SE34I.5 into 8 ohms is about 5.7 damping factor. Of course there is the inconvenient truth that a speakers resistance rises and falls through it's frequency response. At resonance the speaker is more likely to be around 30 ohms not 8 ohms. At 30 ohms the damping factor would rise to between 15 and 21 depending on what position you had the speaker impedance switch set to. Another inconvenient truth is that this simple formula only works with pure resistance, and both the amplifier and the loudspeaker have impedance which is to say resistance, capacitance and inductance. That makes reality 36 times more complicated than the damping formula can predict.
Please read the following excellent explanation:
Click here for a great explanation of damping factor and speaker relationships.
Steve