The keyboardist in my band is also a bass player so he gets it, he just rolls off the bass eq on the board, and doesn't venture down there too much. We actually get a great sound doubling piano/bass parts here and there.
A band I was in had a guitar player with a pretty fancy large 4x12 100w rig, and his sound was mid-scooped and bottom-end heavy, and we ended up having this muddy warbling sound all the time from the low frequencies oscillating.
As for your guy, probably a lost cause. I'd turn down the lows on his amp/board, or have him use an HPF.
A band I was in had a guitar player with a pretty fancy large 4x12 100w rig, and his sound was mid-scooped and bottom-end heavy, and we ended up having this muddy warbling sound all the time from the low frequencies oscillating.
As for your guy, probably a lost cause. I'd turn down the lows on his amp/board, or have him use an HPF.