The Producer speaks
When blending multiple instruments, you must be able not only to hear each instrument. But the tone,depth and brightness of each.
For example: if your are arranging a B3 organ and a bass guitar, you run the risk of falling into a black hole of mud. The two may cancel each other out in spots due to similar tonality.
Coming through my era, the bass was front and center ala Jaco Pastorius, Verdine White, Bootsy Collins, Mark Adams. Bright top, fat bottom.
If you take the Jimmy Smith approach, the B3 will be front and center and bass will take a backseat.
I prefer the Joe Zawinul approach, even though he and Jaco cancelled each other out at times because of ego, that allowed both to shine.
Admittedly Joe was a master of synth and did'nt engage the B3 as much. Listen to the tone and timbre of the instrument and remember to always focus on the song as a whole.
The musical arrangement supports the vocals or the solo instrument. Nobody did this better than producer Maurice White of Earth, Wind & Fire.
The great Larry Dunn on keyboards.
Listen to: Head to the sky, Mighty Mighty, Shining Star.