I'd like to ask you how would you add velocity/volume variation to the kick when making a beat with the SP (404) as the pads are not velocity sensitive.
What I do is play with the mfx12 volume knob but that doesn't sound right
^yup krisso got it, copy it to different pads and change the volume. I'd recommend trying that with all your drum parts to get more dynamic sounding drums. Whenever I chop a break I always have several different copies of each element (snare, hihat, kick, ect.) on different pads at different volumes. It can be fun to mess with the timbre of the copies too, like making some kicks shorter with start/end points or having hits with different isolater settings on them like a bassier kick and a softer more middy kick