What are you trying to achieve? What is your definition of "compact" vs "bookshelf" and why does it matter to you?

BTW, getting a sub to integrate seemlessly with the mains isn't nearly as easy as it sounds. Not only do your mains need to play low enough to reach the crossover point of the sub, but you also have to consider room interaction, nodes, phase, and countless other integration challenges. Fast speakers require fast subs and so on.