You say "So all 24 drives ultimately needs to be connected to the 9260-8i RAID".
Yet, it doesn't matter if they're in the motherboard chassis or JBOD chassis they will ALWAYS be connected to the RAID card doing either of the above mentioned methods.
Avoid the hassle, and get the RAID card that doesn't require 4 adapter cables, and 2 adapters to work
You're working with 24 drives, so no point in making them have numerous points of failure when it can be avoided. What happens if 1 of the external cables gets lose?