From Four 12 inch Woofers To Eight 12 inch Woofers, Will I Get Deeper Bass Or More Bass?

Very sweet speakers - mitch4t
You will achieve more Bass by adding the additional (4) woofers. Are you still using Pass Labs power amps? These speakers crave high power and higher current reserves to reach their peak performance.
Happy Listening!

jafant...I'm very familiar with the Kappa 9 and the power that they require.  That won't be a problem.  I still have the Pass amps.

The whole reason for this approach is to get more bass in the room to emulate the Infinity IRS Beta speakers that I have.  The Betas are excellent speakers....when they are good, but can be inconsistent in the bass area on some recordings and are showing their age (31 years).  The Kappa 9 are extremely consistent on all recordings.  But, the Kappas are no match for the Betas in total bass output and depth (16 hz).  I've entertained adding a pair of subwoofers, but I cannot get a consensus on whether or not a subwoofer will seamlessly integrate.  I do know that adding more of the identical woofers and amplifiers will give seamless integration.  The max I'd like to spend on a pair of subwoofers is $4k period....but, anything but perfect integration is out of the question...I just won't live with that.

Go with subs for deeper base

68pete, according to all the posts I’ve read here on the ’Gon regarding integrating subs into full range speakers seamlessly, it sounds damn near impossible. 

This is for 2-channel listening only...this is not a home theater application.