I would also use a sub with those. Many years ago I bought a pair of CV D-9.(still have them but need surrounds). They should perform similarly to yours. The problem I see here is it depends on how loud you listen. “On paper” the d9 has a sensitivity of 101db and a max output rating of 125db. I’ve never seen anyone test those could surely be fudged. I can say this. Those things could play reeeeeeally damn loud. So I you regularly listen to your Cv’s at very high volumes, you might quickly run out of useful subwoofer output. That’s mostly for music though I’d say. For movies, there’s not a chance that those CV’s can do what a good subwoofer can. Like HD said we don’t know the parameters of the specs and how they were achieved. But a competent HT sub should be solid down to a minimum of 22hz. Some of the larger ones like Rythmiks are tuned to 12hz. For comparison most sealed subs start rolling off between 30-35hz and medium sized ported ones are around 20-22. Cheaper ported ones roll off higher. Normally between 25-30hz. That’s about the range of your CV’s. So while I still absolutely recommend a
sub/s here, I think you’ll need to take a real look at budget. If you’re super strapped, I’d look at the Dayton that mazersteven linked, but iirc the 1200 had better numbers.
If you listen well below the limits of the CV’s then the equation will be different.