I use a current NYC BMP with an LPB1 in front of it set at about 11 o’clock. It doesn’t make the volume any higher when I switch the LPB on but it smooths out and fattens up the Big Muff, making it a little more sludgey through my liove rig (2 x early 70s 100watt Laney Klipp heads).
I doesn’t change the tonality much, but rolling back the tone on my guiatr gives me a perfect doom/stoner tone.
My BMP settings are Volume 3 o’clock, Tone 10 o’clock and Sustain at max.

The LPB after the BMP will boost your volume but at higher setting makes it sound a little too brittle and harsh to my ears. The LPB is a great pedal, as well as fattening up the MUff I use it as a clean boost for quiet songs where I play leads with a totally clean sound.
Buy one!