L Pad Control ruin sound quality???

Hello,
I have a pair of passive subs run through a separate amp all fed from preamp's second set of preamp rca outs,
I was tempted to install an L pad control after the crossover so I can dial in the desired bass level relative to source material.
I get the basic concept that less electronics in the chain so to speak the better.
Beyond that someone told me inserting an L pad into the speaker design effects the control over the woofer, something to do with the damping factor. I'm not a audio tech so this is beyond my comprehension. He also stated the more I reduce the volume the greater the negative effect on speaker control.
Can someone on Agon confirm or refute this concern.

Thanks :)