Are you saying you already use the -15db pad? With MFDs you should use the pad and recover that with the preamp.
What kind of amp are you going into? Try lowering the volume on the bass and turning up the preamp on your amp to see if you get a clean sound that works better. That will give you an idea if you want to let the preamp do more of the work. Even if the light isn’t showing clipping you may not have much headroom left. It depends on the amp. Is it a preamp LED or power amp overload LED, is it a tube preamp or not, etc.
Whatever preamp you have will sound different depending on how hard you hit the front. A lower input signal will let you hear the character of the preamp change more as you turn it up. When it is getting a hot signal up front it may already be saturated and won’t be as flexible. This will be more noticeable in tube pres but will still be a factor with SS.