Thanks for the inputs.
I think I'm going with the Marchand balanced passive filters with a 80hz cross. It's $200 more but fits my connectivity better. What I meant about "a single cap" is its a single connection for me. Inside it's full of components. He offers 30 day returns so I'll order the sub when it arrives and have 30 days to evaluate.
I'm just surprised with all the niche audiophile products out there, only one guy makes these. It makes me wonder whether this is an unusual endeavor in audiophileland. I've seen some previous discussions but no real conclusions. I'll report back when I complete the experiment.