Sub Confusion

Over the years I've always preferred 2 subs, helps solve some bass node issues, but recently have now done without subs. Less integration problems

As rsf507 states, multiple subs tends to resolve node problems. Google "subwoofer swarm" for an explanation for why multiple subs are usually better than one. 

Your reason for wanting to free your speakers from reproducing the lows, is one  great reason for adding subs, Mids and midbass will improve noticeably.

What do you mean when you say you are not looking for 'more bass'? 

I ask, because there is more ambient information in low bass than many people realize. Adding bass down to the lowest octave, opens up the soundstage. 

"My goal is not more base- I’m looking to free my PMCs from having to expend energy to produce sound below 80 Hz and increase depth."

To do that you will need a sub with a high pass filter. You need to use a separate amp and preamp or an integrated with preamp out and amp in!

If you use Rel subwoofers, those don’t have high pass filters!

What Yogiboy said. Adding subs doesn't automatically make life easier for your other components. I think your speakers are transmission line designs. Removing sub-80Hz signals will mess them up. You need to rethink what you're trying to do.