In reply to:

They have a much more rigid, solid cylinder, that many feel tightens up, what is already very tight base with the ultra driver.


That "tightened" sound is what I experienced between my Hsu over the 20-39PC+ and PB12+ in my home.

You should be able to get good money for your 20-39PC+'s on audiogon or HTF.

Your new subs will be quite enjoyable!! What's the next upgrade??