I'm not sold on combo boxes for this. First, there's no way of displaying the SUBCOMPONENT common name. Second, there's no natural way of not choosing one of the subcomponents (I mean, you probably can have an empty row or something, but it's a complete hack). Third, aside from probably looking eye-wateringly ugly , it's going to clash with the check boxes, with both very different looks and modes of interaction, whereas radio buttons blend in, in both of these regards (I'll grant you that whether this is good or bad is probably subjective). Lastly, the longer the subcomponent name, the worse the aesthetics are going to be assaulted (to say nothing of the possibility of combo boxes of different lengths).
1. Don't look without goggles or something: link
; I think it's telling that it is outright difficult to find screenshots of this combination, with most of the hits you do find being horror shows from Windows XP, I mean there
's your stuff of nightmares.