I understand that you like the current sound but you want more bass. If you do not want to get into too much trouble, it is better to add a subwoofer to the equipment, connecting it by High Level: speaker output from the BK power amplifier to the subwoofer and from this to the two KEF.
(https://images.crutchfieldonline.com/ImageBank/v20160824170200/ImageHandler/scale/978/978/core/learn/article/3976/speaker_level_inputs-2.jpg) (https://images.crutchfieldonline.com/ImageBank/v20160824170200/ImageHandler/scale/978/978/core/learn/article/3976/speaker_level_inputs-2.jpg)
I strongly recommend that the chosen subwoofer allows to regulate the phase and not only to switch between 0º and 180º.
Like this Canton:
[IMG] https://www.accessories4less.com/mas_assets/cache/image/3/4/3/2/13362.Jpg