Make cells unavailable for selection based on prev selection.

Hello All,
I'm in the middle of a very big task trying to figure it out.
I've 50 assemblies.. Each have variants. I select Ass#1, for this an option from Ass#2 doesn't support. So should be disabled only for that single option selected in Ass#1.
So I'm trying this in 2 ways.
(1) With drop downs (ComboBox) - eliminating the not required options.
(2) With list as such, trying to deactivate/dim (make disable so as to unable to select) cells required.
Which would make life easier? If either of the above, how could I make cells disabled...
I appreciate any answers in this context...!