OR, run all 6 inputs through an 8-8 belt balancer [feeding 2 spare ouput lanes back in to the spare inputs], then put those 6 outputs into a pair of 3-2 combi belt & lane balancers.

It is *not* input balanced ~ The left & right outside input lanes will drain twice as fast as the inner 4 will.
Would be easier [and smaller] to put a pair of 3>2 belt balancers in at top, then run those 4 outputs through the 4-4 lane balancer. Would be input & output balanced, and count-perfect too.