I finally added a second REL Sub

It's taken me years to get to this point.  Subwoofers were 2-channel system blasphemy when I was coming up in the hobby.  As of today, I now have 2, REL T9is.  They are providing sub-bass and filling out the picture for Klipsch Cornwall IVs.  Even with a loudspeaker as massive and efficient as the Cornwall IV, they fill things out nicely.  

How pleasing it was to hear the two in unison.  I run them so low on crossover and volume that the only thing you hear is sweeter more extended highs against a fuller picture down low.  They are simply not audible in their own right.  Yes, it's true--good sub bass management helps treble and midrange.  

As a hack musician of 20 years or so, I can tune them by ear when I hear a well recorded kick drum, bass guitar and horns.  I tried tuning with mics and software but the good ol' ear does very well here.  

If you're on the fence about one or maybe a second you owe it to yourself to try it.  Is SWARM next? Doubtful.  This is, however, very pleasing indeed.