I should add the connections I suggested, would assume running the Proacs full range with the sub filling in the bottom. This preserves the signal purity to the Proacs.
If you wanted to limit the low frequency to the Proacs, you would need to run your main speaker cables to the sub. The another set of cables from the sub to your Proacs.
If you wanted to limit the low frequency to the Proacs, you would need to run your main speaker cables to the sub. The another set of cables from the sub to your Proacs.